Folic acid supplementation during pregnancy for maternal health and pregnancy outcomes

  • Review
  • Intervention

Authors


Abstract

Background

During pregnancy, fetal growth causes an increase in the total number of rapidly dividing cells, which leads to increased requirements for folate. Inadequate folate intake leads to a decrease in serum folate concentration, resulting in a decrease in erythrocyte folate concentration, a rise in homocysteine concentration, and megaloblastic changes in the bone marrow and other tissues with rapidly dividing cells

Objectives

To assess the effectiveness of oral folic acid supplementation alone or with other micronutrients versus no folic acid (placebo or same micronutrients but no folic acid) during pregnancy on haematological and biochemical parameters during pregnancy and on pregnancy outcomes.

Search methods

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 December 2012) and we contacted major organisations working in micronutrient supplementation, including UNICEF Nutrition Section, World Health Organization (WHO) Maternal and Reproductive Health, WHO Nutrition Division, and National Center on Birth defects and Developmnetal Disabilities, US Centers for Disease Control and Prevention (CDC).

Selection criteria

All randomised, cluster-randomised and cross-over controlled trials evaluating supplementation of folic acid alone or with other micronutrients versus no folic acid (placebo or same micronutrients but no folic acid) in pregnancy.

Data collection and analysis

Two review authors independently assessed trials for inclusion, assessed risk of bias and extracted data. Data were checked for accuracy.

Main results

Thirty-one trials involving 17,771 women are included in this review. This review found that folic acid supplementation has no impact on pregnancy outcomes such as preterm birth (risk ratio (RR) 1.01, 95% confidence interval (CI) 0.73 to 1.38; three studies, 2959 participants), and stillbirths/neonatal deaths (RR 1.33, 95% CI 0.96 to 1.85; three studies, 3110 participants). However, improvements were seen in the mean birthweight (mean difference (MD) 135.75, 95% CI 47.85 to 223.68). On the other hand, the review found no impact on improving pre-delivery anaemia (average RR 0.62, 95% CI 0.35 to 1.10; eight studies, 4149 participants; random-effects), mean pre-delivery haemoglobin level (MD -0.03, 95% CI -0.25 to 0.19; 12 studies, 1806 participants), mean pre-delivery serum folate levels (standardised mean difference (SMD) 2.03, 95% CI 0.80 to 3.27; eight studies, 1250 participants; random-effects), and mean pre-delivery red cell folate levels (SMD 1.59, 95% CI -0.07 to 3.26; four studies, 427 participants; random-effects). However, a significant reduction was seen in the incidence of megaloblastic anaemia (RR 0.21, 95% CI 0.11 to 0.38, four studies, 3839 participants).

Authors' conclusions

We found no conclusive evidence of benefit of folic acid supplementation during pregnancy on pregnancy outcomes.

Résumé scientifique

Supplémentation en acide folique durant la grossesse pour la santé maternelle et les résultats de la grossesse

Contexte

Durant la grossesse, la croissance fœtale provoque une augmentation du nombre total de cellules qui se divisent rapidement, ce qui accroît les besoins en folate. Un apport insuffisant en folate conduit à une réduction de la concentration en folate sérique, ce qui entraîne une réduction de la concentration en folate érythrocytaire, une augmentation de la concentration en homocystéine, et des changements mégaloblastiques de la moelle osseuse et des autres tissus dont les cellules se divisent rapidement

Objectifs

Évaluer l'efficacité de la supplémentation en acide folique seul ou associé à d'autres micronutriments par rapport à l'absence d'acide folique (placebo ou mêmes micronutriments, mais sans acide folique) durant la grossesse sur les paramètres hématologiques et biochimiques durant la grossesse et sur les résultats de la grossesse.

Stratégie de recherche documentaire

Nous avons effectué des recherches dans le registre des essais cliniques du groupe Cochrane sur la grossesse et la naissance (31 décembre 2012) et nous avons contacté les organisations majeures travaillant sur la supplémentation en micronutriments, notamment la Section Nutrition de l'UNICEF, le pôle Santé maternelle et reproductive de l'Organisation mondiale de la Santé (OMS), la Division Nutrition de l'OMS, et le National Center on Birth defects and Developmnetal Disabilities et les US Centers for Disease Control and Prevention (CDC).

Critères de sélection

Tous les essais contrôlés randomisés, randomisés en grappes et croisés évaluant la supplémentation en acide folique seul ou en combinaison avec d'autres micronutriments par rapport à l'absence d'acide folique (placebo ou mêmes micronutriments, mais sans acide folique) au cours de la grossesse.

Recueil et analyse des données

Deux auteurs de la revue ont sélectionné les essais à inclure, évalué les risques de biais et extrait des données, de manière indépendante. L'exactitude des données a été vérifiée.

Résultats principaux

Trente-et-un essais portant sur 17 771 femmes ont été inclus dans cette revue. Cette revue a trouvé que la supplémentation en acide folique n'a aucun impact sur les résultats de la grossesse tels que les naissances prématurées (risque relatif (RR) 1,01, intervalle de confiance (IC) à 95 % 0,73 à 1,38 ; trois études, 2 959 participantes), et les mortinaissances/décès néonataux (RR 1,33, IC à 95 % 0,96 à 1,85 ; trois études, 3 110 participantes). Cependant, on a observé des améliorations du poids de naissance moyen (différence moyenne (DM) 135,75, IC à 95 % 47,85 à 223,68). Par ailleurs, la revue n'a trouvé aucun impact sur l'amélioration de l'anémie pré-accouchement (RR moyen 0,62, IC à 95 % 0,35 à 1,10 ; huit études, 4 149 participantes ; effets aléatoires), le taux d'hémoglobine moyen pré-accouchement (DM -0,03, IC à 95 % -0,25 à 0,19 ; 12 études, 1 806 participantes), les taux de folate sérique moyens pré-accouchement (différence moyenne standardisée (DMS) 2,03, IC à 95 % 0,80 à 3,27 ; huit études, 1 250 participantes ; effets aléatoires), et les taux de folate érythrocytaire moyens pré-accouchement (DMS 1,59, IC à 95 % -0,07 à 3,26 ; quatre études, 427 participantes ; effets aléatoires). Cependant, on a observé une réduction significative de l'incidence de l'anémie mégaloblastique (RR 0,21, IC à 95 % 0,11 à 0,38, quatre études, 3 839 participantes).

Conclusions des auteurs

Nous n'avons découvert aucune preuve concluante concernant le bénéfice de la supplémentation en acide folique durant la grossesse sur les résultats de la grossesse.

アブストラクト

母体の健康および妊娠アウトカムに対する妊娠中の葉酸補充

背景

妊娠中は、胎児の成長が分裂細胞の総数を急速に増加させるため、葉酸塩要求量が増加する。葉酸塩摂取量が不足すると血清葉酸塩濃度が低下するため赤血球中の葉酸塩濃度が低下し、ホモシステイン濃度が上昇し、骨髄および他の組織で急速な細胞分裂を伴う巨赤芽球の変化が認められる。

目的

妊娠中に葉酸を単独でまたは他の微量栄養素と併せて経口補充した場合と葉酸を補充しなかった場合(プラセボ、または葉酸を除く同一の微量栄養素)の、妊娠中の血液学的・生化学的パラメーターおよび妊娠アウトカムに対する有効性を比較評価すること。

検索戦略

Cochrane Pregnancy and Childbirth Group’s Trials Register(2012年12月31日)を検索し、微量栄養素補充に取り組んでいるUNICEF Nutrition Section、世界保健機関(WHO)Maternal and Reproductive Health、WHO Nutrition Division、National Center on Birth defects and Developmnetal Disabilities、米国疾病管理予防センター(CDC)などの主要機関に問い合わせた。

選択基準

妊娠中に葉酸を単独または他の微量栄養素と併せて補充した場合を葉酸を補充しない場合(プラセボ、または葉酸を除く同一の微量栄養素)と比較評価したすべてのランダム化比較試験(RCT)、クラスターランダム化比較試験およびクロスオーバー比較試験。

データ収集と分析

2名のレビューア著者が独立して対象試験およびバイアスのリスクを評価し、データを抽出した。 データの精度を確認した。

主な結果

本レビューでは、17,771例の女性を対象とした31件の試験を対象とした。本レビューでは、葉酸補充が早産(リスク比[RR]1.01, 95%信頼区間[CI]0.73〜1.38、研究数3件、参加者2959例)および死産/新生児死亡(RR 1.33, 95%CI 0.96〜1.85、研究数3件、参加者3110例)などの妊娠アウトカムに影響を与えないことが明らかになった。しかし、平均出生時体重に改善が認められた(平均差[MD]135.75, 95%CI 47.85〜223.68)。一方で、本レビューでは、出生前貧血(平均RR 0.62, 95%CI 0.35〜1.10、研究数8件、参加者4149例、ランダム効果)、出生前ヘモグロビン濃度平均値(MD -0.03, 95%CI -0.25〜0.19、研究数12件、参加者1806例)、出生前血清葉酸塩濃度平均値(標準化平均差[SMD]2.03, 95%CI 0.80〜3.27、研究数8件、参加者1250例、ランダム効果)および出生前赤血球葉酸塩濃度平均値(SMD 1.59, 95%CI -0.07〜3.26、研究数4件、参加者427例、ランダム効果)の改善に影響を与えないことが明らかになった。しかし、巨赤芽球性貧血発生率の低下に有意性が認められた(RR 0.21, 95%CI 0.11〜0.38研究数4件、参加者3839例)。

著者の結論

妊娠アウトカムに対する妊娠中の葉酸補充の有益性に関する決定的なエビデンスを得ることはできなかった。

訳注

《実施組織》厚生労働省「「統合医療」に係る情報発信等推進事業」(eJIM:http://www.ejim.ncgg.go.jp/)[2016.1.2]
《注意》この日本語訳は、臨床医、疫学研究者などによる翻訳のチェックを受けて公開していますが、訳語の間違いなどお気づきの点がございましたら、eJIM事務局までご連絡ください。なお、2013年6月からコクラン・ライブラリーのNew review, Updated reviewとも日単位で更新されています。eJIMでは最新版の日本語訳を掲載するよう努めておりますが、タイム・ラグが生じている場合もあります。ご利用に際しては、最新版(英語版)の内容をご確認ください。

Plain language summary

Folic acid supplementation in pregnancy

Folate is a naturally occurring vitamin while folic aid is the synthetic replacement of folate used in most supplements and in fortified foods. Folate is essential as its deficiency can be caused by poor dietary intake, genetic factors or the interaction between genetic factors and the environment. Women with sickle cell disease and those women in areas where malaria is endemic have a greater need for folate and in these areas anaemia can be a major health problem during pregnancy. Women need more folate in pregnancy to meet their need for extra blood and to meet the growing baby's need for blood. Without adequate folate intake in a mother's diet, she can become anaemic and this can contribute to her baby being small, anaemic and born too early (preterm birth). Folic acid supplementation taken before conception can reduce the chance of the baby having neural tube defects. This review looked to see if taking folic acid supplements during pregnancy could reduce the chance of the baby being born too early and of low birthweight and to see its impact on the mother’s blood (hematological values), folate levels and on pregnancy complications.

The review authors found 31 trials (involving 17,771 women) that looked at the impact of providing folic acid supplementation during pregnancy. The data showed that taking folate during pregnancy was not associated with reducing the chance of preterm births, stillbirths, neonatal deaths, low birthweight babies, pre-delivery anaemia in the mother or low pre-delivery red cell folate, although pre-delivery serum levels were improved. The review also did not show any impact of folate supplementation on improving mean birthweight and the mother’s mean haemoglobin levels during pregnancy compared with taking a placebo. However, the review showed some benefit in indicators of folate status in the mother. The evidence provided so far from these trials did not find conclusive results for any overall benefit of folic acid supplementation during pregnancy.

Most of the studies were conducted over 30 to 45 years ago.

Résumé simplifié

Supplémentation en acide folique durant la grossesse

Le folate est une vitamine naturelle tandis que l'acide folique est le succédané synthétique du folate utilisé dans plupart des compléments alimentaires et des aliments enrichis. Le folate est essentiel, car sa carence peut être due à un apport alimentaire insuffisant, à des facteurs génétiques ou à l'interaction entre les facteurs génétiques et l'environnement. Les femmes atteintes de drépanocytose et les femmes vivant dans des régions où la malaria est endémique ont davantage de besoins en folate, et dans ces régions, l'anémie peut être un problème de santé majeur durant la grossesse. Au cours de la grossesse, les femmes ont davantage de besoins en folate pour satisfaire leurs besoins en sang supplémentaire et les besoins en sang du bébé qui se développe. Sans apport suffisant en folate dans son alimentation, la mère peut devenir anémiée et cela peut contribuer à la naissance d'un bébé de petit poids, anémié et prématuré. La supplémentation en acide folique avant la conception peut réduire le risque de lésions du tube neural chez le bébé. Cette revue a cherché à déterminer si la supplémentation en acide folique durant la grossesse pouvait réduire le risque de naissance d'un bébé prématuré et de petit poids, et à déterminer son impact sur le sang de la mère (valeurs hématologiques), les taux de folate et les complications de grossesse.

Les auteurs de la revue ont trouvé 31 essais (portant sur 17 771 femmes) qui examinaient l'impact de la supplémentation en acide folique durant la grossesse. Les données ont révélé que la supplémentation en folate durant la grossesse n'était pas associée à une réduction du risque de naissances prématurées, de mortinaissances, de décès néonataux, de bébés de faible poids, d'anémie pré-accouchement chez la mère ou de faible taux de folate érythrocytaire pré-accouchement, bien que les taux sériques pré-accouchement aient été améliorés. Par ailleurs, cette revue n'a montré aucun impact de la supplémentation en folate sur l'amélioration du poids de naissance moyen et sur les taux d'hémoglobine moyens de la mère durant la grossesse par rapport à un placebo. Cependant, la revue a montré un certain bénéfice sur les indicateurs du statut du folate chez la mère. A ce jour, les données issues de ces essais n'ont pas permis d'obtenir de résultats concluants indiquant un quelconque effet bénéfique global de la supplémentation en acide folique durant la grossesse.

La majorité des études ont été réalisées il y a plus de 30 à 45 ans.

Notes de traduction

Cette revue a été rédigée pour mettre à jour la revue publiée précédemment, « Supplémentation en folate durant la grossesse », qui a été retirée de la publication dans le numéro 3, 2006, de The Cochrane Library en raison de son obsolescence. Voir Autres versions publiées de cette revue.

Traduit par: French Cochrane Centre 22nd March, 2013
Traduction financée par: Instituts de Recherche en Sant� du Canada, Minist�re de la Sant� et des Services Sociaux du Qu�bec, Fonds de recherche du Qu�bec-Sant� et Institut National d'Excellence en Sant� et en Services Sociaux pour la France: Minist�re en charge de la Sant�

Laički sažetak

Uzimanje folne kiseline u trudnoći

Folat je prirodni oblik vitamina, dok je folna kiselina umjetni nadomjestak za folat koji se koristi u većini pripravaka i ponekad kao dodatak hrani. Folat je nužan za normalno funkcioniranje organizma, a njegov nedostatak nastaje zbog loše prehrane, genetskih čimbenika ili kombinacije utjecaja iz okoliša i genetike. Žene koje boluju od srpaste anemije i one koje žive u područjima zahvaćenim malarijom imaju veću potrebu za folatom i u tim područjima se često javlja anemija tijekom trudnoće. Ženama tijekom trudnoće treba više folata zbog povećane proizvodnje krvnih stanica, kao i sve većim potrebama djeteta. Ako majka hranom ne uzima prikladne količine folata, može postati anemična, što može poremetiti rast djeteta, uzrokovati anemiju i prijevremeno rođenje djeteta. Uzimanje folne kiseline prije začeća može smanjiti vjerojatnost nastanka anomalija živčanog sustava (defekti neuralne cijevi). U ovom Cochrane sustavnom pregledu analizirano je može li uzimanje folne kiseline tijekom trudnoće smanjiti vjerojatnost prijevremenog rođenja djeteta i nedostatne porođajne težine te može li imati utjecaj na majčinu krv (vrijednosti krvnih testova), razinu folata i komplikacije u trudnoći.

Autori su pronašli 31 kliničku studiju (s ukupno 17771 žena), u kojima je istražen utjecaj uzimanja folne kiseline tijekom trudnoće. Podatci su pokazali da uzimanje folata tijekom trudnoće nije povezano sa smanjenom vjerojatnošću prijevremenog rođenja, mrtvorođenosti, smrti novorođenčadi, niske porođajne težine, anemije majke prije porođaja niti niske razine folata u crvenim krvnim zrncima prije rođenja – iako se poboljšala razina folata u krvnom serumu prije porođaja. Sustavni pregled je pokazao da nadomjestci folata poboljšavaju prosječnu porođajnu težinu djeteta te da značajno smanjuju pojavu megaloblastične anemije kod majki. Podatci iz ovog Cochrane sustavnog pregleda nisu pokazali uvjerljive dokaze za korist od uzimanje folata za poboljšanje zdravlja majke i ishode trudnoće.

Većina istraživanja provedena je prije 30-45 godina.

Bilješke prijevoda

Prevoditelj:: Croatian Branch of the Italian Cochrane Centre

平易な要約

妊娠中の葉酸補充

葉酸塩は天然のビタミンで、葉酸は多数のサプリメントや栄養素強化食品に使用される葉酸塩の合成代替品である。葉酸塩は必須栄養素であり、食事摂取量不足、遺伝的素因または遺伝的素因間の相互作用および環境によって欠乏症が発生する。鎌状赤血球病の女性およびマラリア流行地域の女性は葉酸塩の要求量が高く、これらの地域では妊娠中の貧血が大きな健康上の問題となっている。母体が余分に必要としている血液や発育中の胎児が必要としている血液の需要を満たすため、女性は妊娠中により多くの葉酸塩を必要とする。母親が食事から十分量の葉酸塩が摂取しないと母体に貧血がおこるため、胎児は小さく、貧血状態で、予定日よりかなり早く生まれる(早産)。受胎前の葉酸補充は、胎児が神経管欠損症を発症する確率を低下させる。このレビューでは、妊娠中の葉酸補充が早産や低出生体重児の発生率を低下させるかどうかを、また、妊娠中の葉酸補充が母親の血液(血算値)、血中葉酸塩濃度および妊娠合併症に及ぼす影響を検証した。

レビュー著者は、妊娠中の葉酸補充の影響を検証した31件の試験(17,771人の女性が参加)を探し出した。試験データから、妊娠中の葉酸塩摂取は早産、死産、新生児死亡、低出生体重児、母親の出生前貧血または出生前赤血球葉酸塩濃度の低値とは関連していないが、出生前血清葉酸塩濃度を改善することが示された。このレビューでは、葉酸塩補充とプラセボを比較した結果、平均出生時体重および妊娠中の母親の平均ヘモグロビン濃度の改善に対する影響は認められなかった。しかし、このレビューでは母親の葉酸塩充足状態の指標に対する有益性が示された。現時点では、今回対象とした試験から得られたエビデンス(証拠)からは、妊娠中の葉酸補充の総合的な有益性を示す決定的な結果は得られなかった。

大部分の研究は30年から45年以上前に実施された。

訳注

《実施組織》厚生労働省「「統合医療」に係る情報発信等推進事業」(eJIM:http://www.ejim.ncgg.go.jp/)[2016.1.2]
《注意》この日本語訳は、臨床医、疫学研究者などによる翻訳のチェックを受けて公開していますが、訳語の間違いなどお気づきの点がございましたら、eJIM事務局までご連絡ください。なお、2013年6月からコクラン・ライブラリーのNew review, Updated reviewとも日単位で更新されています。eJIMでは最新版の日本語訳を掲載するよう努めておりますが、タイム・ラグが生じている場合もあります。ご利用に際しては、最新版(英語版)の内容をご確認ください。

Background

Description of the intervention

Folate is a generic term for both the endogenous form of the vitamin occurring naturally in food and the synthetic form found in supplements and fortified foods (Bailey 1995). It should be noted, however, that folate is a naturally occurring vitamin while folic aid is the synthetic replacement of folate used in most supplements and in fortified foods. Humans are fully dependent on dietary sources or dietary supplements and microorganisms in their intestinal tract for their folate supply. Folate derivatives are essential for the synthesis of nucleic acid, amino acids, cell division, tissue growth, and DNA methylation (Krishnaswamy 2001; Morrison 1998; Scholl 2000).

Inadequate folate intake leads to a decrease in serum folate concentration, resulting in a decrease in erythrocyte (red blood cell) folate concentration, a rise in homocysteine (Hcy) concentration, and megaloblastic changes in the bone marrow and other tissues with rapidly dividing cells (Dietary Ref 1998; Willoughby 1968). During pregnancy, fetal growth causes an increase in the total number of rapidly dividing cells, which leads to increased requirements for folate (Bailey 1995). With inadequate folic acid intake, concentrations of folate in maternal serum, plasma, and red blood cells decrease from the fifth month of pregnancy onwards (Açkurt 1995; Bates 1986). If inadequate folate intake is sustained during pregnancy, megaloblastic anaemia (a blood disorder characterised by anaemia, with red blood cells that are larger than normal and cell contents that are not completely developed) occurs (Willoughby 1968). Folate concentrations continue to decrease for several weeks after pregnancy (Bruinse 1995; Smith 1983), and by the second to third month postpartum, a third of all mothers can have subnormal concentrations of folate in serum and red blood cells (Açkurt 1995). Possible causes for the decline in blood folate during pregnancy include increased folate demand for growth of the fetus due to an increase in the number of rapidly dividing cells (Bailey 1995) and growth of uteroplacental organs, decreased folate absorption, low folate intake, hormonal influence on folate metabolism as a physiologic response to pregnancy (Chanarin 1969), and dilution of folate due to blood volume expansion (Bruinse 1995). Folate demands may be further increased in women with sickle cell disease and women living in areas where malaria is endemic (Lawson 1988); in these areas, anaemia in pregnancy is a major health problem. Increased folate catabolism and urinary folate excretion (Fleming 1972; Landon 1971) may also contribute to increased folate needs in pregnancy (Caudill 1998; Gregory 2001b; Higgins 2000; McPartlin 1993), but the findings are controversial. As a consequence of folate deficiency, Hcy accumulates in the serum and is found to be associated with an increased risk in cardiovascular disease (Refsum 2008), late pregnancy complications such as pre-eclampsia (Makedos 2007; Patrick 2004; Tamura 2006), and neural tube defects around the time of conception (De Benoist 2008).

The recommended folate intake for pregnant women is 400 µg/day (Food and Nutrition Board 1970). It was revised in 1999 after evaluating its bioavailability from food and synthetic folate, and the recommendation was increased to 450 µg (600 DFEs/day (dietary folate equivalent)) (Institute of Medicine 2000). It should be noted that as per NICE guidelines, this amount of folic acid when supplemented to pregnant women (and those intending to become pregnant), before conception and throughout the first 12 weeks, reduces the risk of having a baby with a neural tube defect (NICE 2008). However, the Food and Nutrition Board of the Institute of Medicine have suggested that an increased folate intake might delay the diagnosis of vitamin B-12 deficiency by correcting the anaemia, or even exacerbate its neurologic and neuropsychiatric effects (Food and Nutrition Board 1998; Herbert 1997; Rush 1994). Further research is still needed in this area.

How the intervention might work

The relationship between pregnancy outcome and maternal blood folate concentrations, folate intake and hyperhomocysteinaemia cannot be ignored (Smits 2001). Plasma total homocysteine (tHcy) is regulated by folate status (Selhub 1993), and hyperhomocysteinaemia is linked to vaso-occlusive disease (Green 1995). Impaired placental perfusion due to hyperhomocysteinaemia is implicated in having a negative effect on pregnancy outcome, as are inadequate folate intake and low serum folate concentrations (Scholl 2000). Folate has long been used as a supplement in combination with iron during pregnancy, largely on the basis of haematological benefits (Fleming 1968), although deficiency has also been associated with pregnancy complications and congenital malformations (Scholl 2000). Periconceptional supplementation with folic acid, three months before and early in pregnancy is recommended (Czeizel 1992; MRC 1991), and has been shown to reduce the risk of neural tube defects by almost three-quarters (De-Regil 2010). Although still unproven, folic acid supplementation has also been suggested to help prevent other fetal malformations such as congenital heart defects (Botto 1996; Czeizel 1993; Czeizel 1996; Shaw 1995), urinary tract anomalies (Li 1995), limb defects (Czeizel 1993), oro-facial clefts (Czeizel 1993; Li 1995; Shaw 1995), and pyloric stenosis (Shaw 1995).

Why it is important to do this review

The role of folate deficiency in increasing the risk of spontaneous abortion and birth outcomes such as low birthweight, preterm birth, and perinatal mortality is unclear (Bukowski 2009; Scholl 2000). Hence, the aim of this review is to assess the effect of folic acid supplementation alone in pregnant women on haematological and biochemical parameters, adverse events during pregnancy, and on pregnancy outcomes. We did not assess periconceptional folic acid supplementation, or supplementation of folic acid along with iron during pregnancy and with other micronutrients, as these have been addressed by other reviews (Haider 2006; De-Regil 2010; Pena-Rosas 2006).

Objectives

To assess the effectiveness of oral folic acid supplementation alone or with other micronutrients versus no folic acid (placebo or same micronutrients but no folic acid) during pregnancy on haematological and biochemical parameters during pregnancy and on pregnancy outcomes.

Methods

Criteria for considering studies for this review

Types of studies

We included randomised or quasi-randomised controlled trials of folic acid supplementation alone or with other micronutrients versus no folic acid (placebo or same micronutrients but no folic acid).

Types of participants

We included pregnant women of any age and parity.

Types of interventions

  1. Folic acid alone versus no treatment/placebo (no folic acid)

  2. Folic acid+ iron versus iron (no folic acid)

  3. Folic acid + other vitamins and minerals versus other vitamins and minerals (but no folic acid)

We excluded studies that supplemented folic acid in the form of fortification or home fortification alone or in combination with other micronutrients. We also excluded studies in which women were supplemented during periconception.

Types of outcome measures

Primary outcomes
Maternal outcomes
  • Pre-delivery anaemia (less than 10 g/dL haemoglobin or haematocrit below 30%

  • Mean pre-delivery haemoglobin level

  • Low pre-delivery serum folate (less than 3 mg/L or 7 nmol/L or 3 ng/mL)

  • Mean pre-delivery serum folate level

  • Low pre-delivery red cell folate (less than 100 mg/L or 300 nmol/L or 140 ng/mL)

  • Mean pre-delivery red cell folate

Pregnancy outcome
  • Preterm birth (delivery before 37 weeks of gestation)

Infant outcome
  • Low birthweight (birthweight less than 2500 g)

Secondary outcomes
  • Miscarriage (loss of pregnancy before 22 weeks of gestation)

  • Perinatal mortality - includes stillbirth (deaths after 22 weeks of gestation) and mortality in the first seven days of life

  • Pre-eclampsia- defined as blood pressure of > 140 mmHg systolic or > 90 mmHg diastolic after 20 weeks of gestation, and proteinuria of more than 0.3 g in 24 hours

  • Respiratory disease in child

  • Allergic disease in child

  • Megaloblastic anaemia

  • Hyperhomocysteinaemia (more than 16 micromol/L)

Search methods for identification of studies

Electronic searches

We contacted the Trials Search Co-ordinator to search the Cochrane Pregnancy and Childbirth Group’s Trials Register (31 December 2012)

The Cochrane Pregnancy and Childbirth Group’s Trials Register is maintained by the Trials Search Co-ordinator and contains trials identified from:

  1. monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL);

  2. weekly searches of MEDLINE;

  3. weekly searches of EMBASE;

  4. handsearches of 30 journals and the proceedings of major conferences;

  5. weekly current awareness alerts for a further 44 journals plus monthly BioMed Central email alerts.

Details of the search strategies for CENTRAL, MEDLINE and EMBASE, the list of handsearched journals and conference proceedings, and the list of journals reviewed via the current awareness service can be found in the ‘Specialized Register’ section within the editorial information about the Cochrane Pregnancy and Childbirth Group.

Trials identified through the searching activities described above are each assigned to a review topic (or topics). The Trials Search Co-ordinator searches the register for each review using the topic list rather than keywords. 

Searching other resources

For identification of ongoing or unpublished studies, we contacted major organisations working in micronutrient supplementation, including UNICEF Nutrition Section, World Health Organization (WHO) Maternal and Reproductive Health, WHO Nutrition Division, and National Center on Birth defects and Developmnetal Disabilities, US Centers for Disease Control and Prevention (CDC).

We did not apply any language restrictions.

Data collection and analysis

Selection of studies

Two review authors, Zohra Lassi (ZSL) and Rehana Salam (RAS), independently assessed for inclusion all the potential studies we identified as a result of the search strategy. We resolved any disagreement through discussion and, if required, we consulted the third review author, Zulfiqar Bhutta (ZAB)

Data extraction and management

We designed a form to extract data. For eligible studies, two review authors (RAS and ZL) extracted the data using the agreed form. We resolved discrepancies through discussion and, if required, we consulted the third review author. Data were entered into ReviewManager software (RevMan 2011) and checked for accuracy.

When information regarding any of the above was unclear, we attempted to contact authors of the original reports to provide further details.

Assessment of risk of bias in included studies

Two review authors (ZSL and RAS) independently assessed risk of bias for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). Any disagreement was resolved by discussion or by involving a third assessor (ZAB).

(1) Random sequence generation (checking for possible selection bias)

We described for each included study the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it produced comparable groups. We assessed the method as:

  • low risk of bias (any truly random process, e.g. random number table; computer random number generator);

  • high risk of bias (any non-random process, e.g. odd or even date of birth; hospital or clinic record number);

  • unclear risk of bias.

(2) Allocation concealment (checking for possible selection bias)

We described for each included study the method used to conceal the allocation sequence in sufficient detail and determine whether intervention allocation could have been foreseen in advance of, or during recruitment, or changed after assignment.

We assessed the methods as:

  • low risk of bias (e.g. telephone or central randomisation; consecutively numbered sealed opaque envelopes);

  • high risk of bias (open random allocation; unsealed or non-opaque envelopes, alternation; date of birth);

  • unclear risk of bias.   

(3.1) Blinding (checking for possible performance bias)

We described for each included study the methods used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. We considered that studies were at low risk of bias if they were blinded, or if we judged that the lack of blinding would be unlikely to affect results. We assessed blinding separately for different outcomes or classes of outcomes.

We assessed the methods as:

  • low, high or unclear risk of bias for participants;

  • low, high or unclear risk of bias for personnel.

(4) Incomplete outcome data (checking for possible attrition bias through withdrawals, dropouts, protocol deviations)

We described for each included study, and for each outcome or class of outcomes, the completeness of data including attrition and exclusions from the analysis. We stated whether attrition and exclusions were reported, the numbers included in the analysis at each stage (compared with the total randomised participants), reasons for attrition or exclusion where reported, and whether missing data were balanced across groups or were related to outcomes. Where sufficient information was reported, or could be supplied by the trial authors, we re-included missing data in the analyses which we undertook. We assessed methods as:

  • low risk of bias (e.g. no missing outcome data; missing outcome data balanced across groups);

  • high risk of bias (e.g. numbers or reasons for missing data imbalanced across groups; ‘as treated’ analysis done with substantial departure of intervention received from that assigned at randomisation);

  • unclear risk of bias.

(5) Selective reporting bias

We described for each included study how we investigated the possibility of selective outcome reporting bias and what we found.

We assessed the methods as:

  • low risk of bias (where it was clear that all of the study’s pre-specified outcomes and all expected outcomes of interest to the review have been reported);

  • high risk of bias (where not all the study’s pre-specified outcomes have been reported; one or more reported primary outcomes were not pre-specified; outcomes of interest were reported incompletely and so could not be used; study failed to include results of a key outcome that would have been expected to have been reported);

  • unclear risk of bias.

(6) Other bias (checking for bias due to problems not covered by (1) to (5) above)

We described for each included study any important concerns we had about other possible sources of bias.

We assessed whether each study was free of other problems that could put it at risk of bias:

  • low risk of other bias;

  • high risk of other bias;

  • unclear whether there is risk of other bias.

(7) Overall risk of bias

We made explicit judgements about whether studies were at high risk of bias, according to the criteria given in the Handbook (Higgins 2011). With reference to (1) to (6) above, we assessed the likely magnitude and direction of the bias and whether we considered it was likely to impact on the findings. 

Measures of treatment effect

Dichotomous data

For dichotomous data, we presented results as summary risk ratio with 95% confidence intervals. 

Continuous data

For continuous data, we used the mean difference if outcomes were measured in the same way between trials. We used the standardised mean difference to combine trials that measured the same outcome, but used different methods.  

Unit of analysis issues
Cluster-randomised trials

We included cluster-randomised/quasi-randomised trials in the analyses along with individually-randomised trials. We incorporated the data of cluster-randomised/quasi-randomised trials using generic inverse variance method in which logarithms of risk ratio estimates were used along with the standard error of the logarithms of risk ratio estimates.

Cross-over trials

We also looked for any cross-over trials on this topic, and such trials were deemed eligible for inclusion, However, we did not find any eligible cross-over trials.

Dealing with missing data

We noted levels of attrition for included studies. We also planned to explore the impact of including studies with high levels of missing data in the overall assessment of treatment effect by using sensitivity analysis. For all outcomes, we carried out analyses, as far as possible, on an intention-to-treat basis, i.e. we attempted to include all participants randomised to each group in the analyses, and all participants were analysed in the group to which they were allocated, regardless of whether or not they received the allocated intervention. The denominator for each outcome in each trial was the number randomised minus any participants whose outcomes were known to be missing.

Assessment of heterogeneity

We assessed statistical heterogeneity in each meta-analysis using the T², I² and Chi² statistics. We regarded heterogeneity as substantial if the I² was greater than 30% and either T² was greater than zero, or there was a low P value (less than 0.10) in the Chi² test for heterogeneity. 

Assessment of reporting biases

If there were 10 or more studies in the meta-analysis, we investigated reporting biases (such as publication bias) using funnel plots. We assessed funnel plot asymmetry visually, If asymmetry was suggested by a visual assessment, we performed exploratory analyses to investigate it.

Mostly studies were old and we suspected reporting bias, therefore, we attempted to contact study authors, where possible, asking them to provide missing outcome data.

Data synthesis

We carried out statistical analysis using the Review Manager software (RevMan 2011). We used fixed-effect Mantel-Hanzel meta-analysis for combining data where it was reasonable to assume that studies were estimating the same underlying treatment effect: i.e. trials were examining the same intervention, and the trials’ populations and methods were judged to be sufficiently similar. If there was clinical heterogeneity sufficient to expect that the underlying treatment effects differed between trials, or if substantial statistical heterogeneity was detected, we used random-effects meta-analysis to produce an overall summary if an average treatment effect across trials was considered clinically meaningful. The random-effects summary was treated as the average range of possible treatment effects and we discussed the clinical implications of treatment effects differing between trials. If the average treatment effect was not clinically meaningful, we did not combine trials.

If we used random-effects analyses, the results were presented as the average treatment effect with 95% confidence intervals, and the estimates of  T² and I².

Subgroup analysis and investigation of heterogeneity

We planned to carry out subgroup analyses based on following factors.

• Different doses of folate used (< 400 μg and > 400 μg)
• Different durations of folate supplementation
• Haemoglobin level of participants
• Co-interventions

Not all included studies mentioned the baseline haemoglobin levels of participants and since duration and start of folic acid supplementation in women during pregnancy varied, we, therefore, did not carry out these subgroup analyses. However, subgroup analyses were carried out on studies in which iron was additionally provided with folic acid. We also performed subgroup analyses on the dosage of folic acid.

We also reported the outcomes based on how the outcome was defined in the individual study.

We assessed subgroup differences by the interaction tests available within RevMan (RevMan 2011). We reported the results of subgroup analyses quoting the χ² statistic and the P value, and the interaction test I² value.

Sensitivity analysis

We did not perform sensitivity analyses as studies were old and of mediocre quality.

Results

Description of studies

Results of the search

A total of 94 trial reports were considered for inclusion into this review, finally 31 studies involving 17,771 women were included in this review (Figure 1).

Figure 1.

Study flow diagram.

Included studies

Thirty-one studies have been included in this review. The majority of these studies were quite old and were conducted during the 1960s (Castren 1968; Chanarin 1965; Chanarin 1968; Chisholm 1966; Dawson 1962; Edelstein 1968; Fleming 1968; Hibbard 1969a; Menon 1962; Metz 1965; Willoughby 1967); the 1970s (Balmelli 1974; Batu 1976; Baumslag 1970; Fletcher 1971; Giles 1971; Iyengar 1975; Rae 1970; Rolschau 1979; Trigg 1976; Weil 1977), and the 1980s (Blot 1981; Harrison 1985; Lira 1989; Roth 1980; Srisupandit 1983; Tchernia 1982; Pack 1980). Three studies were published in 2005 (Charles 2005; Christian 2003; Decsi 2005), however, Charles 2005 re-analysed data that were collected in 1966. Seven studies (Chanarin 1965; Christian 2003; Dawson 1962; Decsi 2005; Hibbard 1969a; Metz 1965; Pack 1980) were were not included in the meta-analyses because they either did not mention their standard deviations/standard errors; or they reported the rise or fall in the haematological and biochemical levels.

Most of the outcomes were defined in the same way across different trials except for preterm birth, pre-delivery anaemia, and low birthweight which were defined differently, however, we still included them and they were presented in subgroup according to their defined cut-offs (Refer to Table 1). The majority of the studies were conducted in Europe (Balmelli 1974; Blot 1981; Castren 1968; Chanarin 1965; Chanarin 1968; Charles 2005; Chisholm 1966; Dawson 1962; Decsi 2005; Fletcher 1971; Hibbard 1969a; Rae 1970; Rolschau 1979; Tchernia 1982; Trigg 1976; Weil 1977; Willoughby 1967), Africa (Baumslag 1970; Edelstein 1968; Fleming 1968; Harrison 1985; Metz 1965) and Asia (Batu 1976; Christian 2003; Iyengar 1975; Menon 1962; Srisupandit 1983). One study was conducted in South America (Lira 1989), one in Australia (Giles 1971) and one in New Zealand (Pack 1980). One study (Roth 1980) did not mention the setting. The time for initiation of supplementation varied from 8th week of pregnancy till three days postpartum. Most of the studies supplemented women with folic acid in combination with iron (Balmelli 1974; Batu 1976; Baumslag 1970; Blot 1981; Castren 1968; Chanarin 1965; Chanarin 1968; Chisholm 1966; Christian 2003; Edelstein 1968; Fletcher 1971; Giles 1971; Harrison 1985; Iyengar 1975; Lira 1989; Menon 1962; Metz 1965; Rae 1970; Rolschau 1979; Roth 1980; Srisupandit 1983; Tchernia 1982; Trigg 1976; Weil 1977; Willoughby 1967) however, only a few compared folic acid alone with placebo (Charles 2005; Chisholm 1966; Decsi 2005; Fleming 1968; Pack 1980).

Table 1. Outcomes definition
StudyPreterm deliveryLow birthweightPerinatal mortalityMiscarriagePre-eclampsiaRespiratory disease in childAllergic disease in childPre-delivery anaemiaLow pre-delivery serum folateLow pre-delivery red cell folateMegaloblastic anaemiaHyperhomocystenaemia
Balmelli 1974--------< 4 µg/L< 150 µg/L--
Batu 1976-------< 10 g/dL-- -
Baumslag 1970------------
Blot 1981< 38 weeks-----------
Castren 1968------------
Chanarin 1965------------
Chanarin 1968------------
Charles 2005-< 2500 g----------
Chisholm 1966-------< 11 g/dL< 2.1 mµg/mL---
Dawson 1962------------
Decsi 2005------------
Edelstein 1968------------
Fleming 1968------------
Fleming 196836-38 weeks< 2500 g----------
Fletcher 1971-------< 11 g/100 mL< 2.5 ng/mL---
Giles 1971-< 2400 g ----< 10 g/100 mL----
Harrison 1985------------
Iyengar 1975-< 2500 g-----< 10.5 g/dL----
Lira 1989------------
Menon 1962;-------< 10.5 g%- --
Metz 1965------------
Pack 1980------------
Rae 1970;------------
Rolschau 1979;------------
Roth 1980;--------< 4 µ/L< 150 µ/L- 
Srisupandit 1983;------- ----
Tchernia 1982;------------
Trigg 1976;------------
Weil 1977;------------
Willoughby 1967-------< 10 g/dL--< 10 g/100 mL-

Please refer to the Characteristics of included studies table for more details.

Excluded studies

A total of 25 studies were excluded from the review as they did not satisfy the inclusion criteria. Hamilton 1973 was not a randomised controlled trial. There were four studies in which folic acid was given in combination with other micronutrients compared with a no supplement group (Bjerre 1967; Ma 2008; Wang 2012; Zeng 2008). Similarly, Giles 1960 compared the intervention group with historical controls; Gregory 2001 compared pregnant women with non pregnant women; Khanna 1977 evaluated the therapeutic use of folic acid in women with anaemia; and there were a few studies in which the association of folic acid supplementation was observed, with breast cancer, fetal apoptosis (Klinger 2006), congenital anomalies (Ulrich 1999) and with malaria when given with sulphadoxine pyrimethamine (Ouma 2006). We excluded studies in which therapy of iron and folic acid was compared with no therapy at all (Taylor 1979; Taylor 1981). We also excluded studies in which folic acid was given in a fortification form (Colman 1974; Colman 1975). We excluded studies that compared the duration of folic acid supplements (Ellison 2004; Polatti 1992), and different dosage of folic acid supplements (Hekmatdoost 2011; Hibbard 1969; Manizheh 2009). Trials were also excluded that were in the form of published abstracts only and had insufficient information to extract (Hague 1998; Kristoffersen 1979; Melli 2008; Thomson 1982). Also, one study in which results from three trials were re analysed was excluded (Tchernia 1982a).

Please refer to Characteristics of excluded studies table for more details.

Risk of bias in included studies

Most of the studies were conducted over 30 to 45 years ago, and we found poor subjective and objective compliance with random allocation, adequate concealment and blinding. Bias and confounding thus seem to us the likely explanation for our findings.

Figure 2 and Figure 3 provide a graphical summary of the results of risk of bias for the included studies.

Figure 2.

Methodological quality graph: review authors' judgements about each methodological quality item presented as percentages across all included studies.

Figure 3.

Methodological quality summary: review authors' judgements about each methodological quality item for each included study.

Allocation

Sequence generation and adequate allocation concealment was a problem in almost all the studies and control of selection bias at entry was often difficult to assess as many authors stated that women were 'randomly allocated' without actually describing the technique, still there were studies that managed to report the methods of allocation concealment adequately (Blot 1981; Edelstein 1968; Fleming 1968; Giles 1971; Rolschau 1979).

Blinding

Blinding was the another issue which was rarely discussed in depth, and only few reported them adequately including Blot 1981; Edelstein 1968; Fleming 1968; Giles 1971; Harrison 1985; Weil 1977.

Incomplete outcome data

Mostly studies provided insufficient information regarding attrition rates, which meant we were unable to make any judgment. There were only a few studies that discussed their exclusion and attrition rates and reported their reasons. (Balmelli 1974; Batu 1976; Blot 1981 Castren 1968; Fleming 1968; Giles 1971 Harrison 1985; Iyengar 1975; Srisupandit 1983; Tchernia 1982).

Selective reporting

Again, studies provided insufficient information, which limited us from making any judgment (Balmelli 1974; Blot 1981; Castren 1968; Harrison 1985; Iyengar 1975; Srisupandit 1983).

Other potential sources of bias

No other bias was identified but we had insufficient information available to fully assess this 'Risk of bias' domain. Consequently, we assessed all included studies as being at 'unclear' risk of other bias.

Effects of interventions

a. Clinical measures of untoward events during pregnancy and of pregnancy outcome

Preterm birth

None of the included studies reported preterm birth in accordance with our definition of the outcome. We found two studies, of which one defined it as birth of a baby between 36 to 38 weeks, and another defined it as birth before 38 weeks of pregnancy. We pooled them both to look for an association with folic acid supplementation in pregnancy. Our analysis showed that administration of folic acid supplementation during pregnancy has no impact on reducing preterm birth (risk ratio (RR) 1.01, 95% confidence interval (CI) 0.73 to 1.38; three studies, 2959 participants (Analysis 1.1)).

Stillbirths/neonatal deaths

None of the included studies reported perinatal mortality. However, three studies reported stillbirth and neonatal mortality as a composite outcome, hence we pooled them to obtain data for perinatal mortality. Folic acid supplementation during pregnancy did not show any impact on reducing stillbirths/neonatal deaths (RR 1.33, 95% CI 0.96 to 1.85; three studies, 3110 participants (Analysis 1.2)).

Birthweight

Folic acid supplementation during pregnancy did not show any impact on reducing low birthweight (less than 2500 g) (RR 0.83, 95% CI 0.66 to 1.04; four studies, 3113 participants (Analysis 1.3)).

We also attempted to look at the impact of folic acid supplementation during pregnancy on mean birthweight (g) of newborns and found no association (mean difference (MD) 104.96 g, 95% CI -0.25.50 g to 235.41 g; five studies, 774 participants; random-effects, T² = 21694.29, I² = 90% (Analysis 1.4)). All the studies pooled for this outcome compared folic acid + iron versus iron alone.

The standard errors for Trigg 1976 were very small as compared to the other trials for being plausible, therefore, we conducted a sensitivity analysis after removing this study. Heterogeneity was reduced from 90% to 50% (MD 135.76, 95% CI 47.85 to 223.68; four studies, 625 participants; random-effects, T² = 4841.10, I² = 50% (Analysis 1.5)

Outcomes not reported in the included studies

The included studies did not report on the impact of folic acid supplementation on miscarriage, pre-eclampsia, respiratory disease or allergic disease in children.

b. Haematological and biochemical parameters

Pre-delivery anaemia

The included studies used different definitions of anaemia. Eight studies reported pre-delivery anaemia as an outcome, but only two studies used our definition of anaemia. We included all studies reporting anaemia but pooled them separately according to the definition of anaemia used. Folic acid supplementation did not show any impact on reducing pre-delivery anaemia (any cut-off point) (average RR 0.62, 95% CI 0.35 to 1.10; eight studies, 4149 participants; random-effects, T² = 0.51, I² = 90% (Analysis 1.6)). When studies were separately pooled according to the definition described in the earlier section of this review, we found that supplementation had no impact on reducing anaemia (haemoglobin less than 10 g/dL) (average RR 0.35, 95% CI 0.05 to 2.42; two studies, 2448 participants; random-effects, T² = 1.86, I² = 97% (Analysis 1.6)).

We also looked at the impact of folic acid supplementation in pregnancy on mean pre-delivery haemoglobin level, and found no difference in the mean haemoglobin concentration among those in the intervention arm compared with those in the placebo arm (MD -0.03, 95% CI -0.25 to 0.19; 12 studies, 1806 participants; random-effects, T² = 0.12, I² = 95% (Analysis 1.7)). All the studies pooled for this outcome compared folic acid + iron versus iron alone.

With regard to subgroup analysis based on dosage of folic acid supplementation, we found no differences on improving haemoglobin concentrations and the interaction test was insignificant (Chi² = 1.18, df = 1 (P = 0.28), I² = 15.1%). Analysis 1.8

We also ran a funnel plot to assess the publication bias and we found studies were equally distributed on each side except for two outliers Figure 4.

Figure 4.

Funnel plot of comparison: 1 Folic acid versus no folic acid, outcome: 1.7 Mean pre-delivery haemoglobin level.

Pre-delivery serum folate

Folic acid supplementation in pregnancy showed a reduction in the incidence of low pre-delivery serum folate by 62% (RR 0.38, 95% CI 0.25 to 0.59; two studies, 696 participants (Analysis 1.11)).

We found non-significantly higher mean pre-delivery serum folate levels among those in the folic acid supplementation arm compared with those in the placebo arm (standardised mean difference (SMD) 2.03, 95% CI 0.80 to 3.27; eight studies, 1250 participants; random-effects, T² = 2.96, I² = 98% (Analysis 1.9)). All the studies pooled for this outcome compared folic acid + iron versus iron alone.

For subgroup analysis based on dosage of folic acid supplementation, we found significant improvements in mean serum folate concentration when the dose was less than 400 μg (SMD 3.70, 95% CI: 0.28 to 7.11, four studies n = 253, random effects, I² = 99%), however, no impact was seen of folic acid > 400 μg (SMD 0.68, 95% CI: -0.75 to 2.10, four studies n = 997, random effects, I² = 98%) Analysis 1.10. The interaction test for the overall estimate was not significant (Chi² P value = 0.11, I² = 61%) suggesting no difference between groups.

Pre-delivery red cell folate

None of the included studies reported data for pre-delivery red cell folate deficiency status. However, mean red cell folate levels were reported in four studies. Folic acid supplementation during pregnancy did not show any impact on reducing mean pre-delivery red cell folate levels (SMD 1.59, 95% CI -0.07 to 3.26; four studies, 427 participants; random-effects, T² = 2.79, I² = 97% (Analysis 1.12)). All the studies pooled for this outcome compared folic acid + iron versus iron alone.

Megaloblastic anaemia

Folic acid supplementation during pregnancy significantly reduced the incidence of megaloblastic anaemia by 79% (RR 0.21, 95% CI 0.11 to 0.38; four studies, 3839 women (Analysis 1.13)).

Outcomes not reported in the included studies

The included studies did not report on the impact of folic acid supplementation on hyperhomocysteinaemia, respiratory disease and allergic disease in the child.

Discussion

Summary of main results

From our meta-analysis of randomised controlled trials on folic acid supplementation, we found no evidence of an effect of supplements on preterm birth, stillbirth/neonatal death, mean birthweight/low birthweight, low pre-delivery haemoglobin and serum red cell folate. However, we found a risk reduction on low pre-delivery serum folate and megaloblastic anaemia.

Quality of the evidence

First, all the included studies were conducted over 30 to 45 years ago, and we found poor subjective and objective compliance with random allocation, adequate concealment and blinding. Bias and confounding thus seem to be the likely explanation for our findings.

Second, for combining studies, it is important that the outcome measures are comparable. Of note, trials included in this analysis reported outcomes quite differently from each other. This could have resulted in higher risk of bias due to selective reporting in these trials. However, we pooled them separately, wherever possible, to minimise this bias.

Potential biases in the review process

We undertook a systematic, thorough search of the literature to identify all studies meeting the inclusion criteria and we are confident that the included trials met the set criteria. Study selection and data extraction were carried out in duplicate and independently and we reached consensus by discussing any discrepancies. A protocol was published for this review. All the analyses were specified a priori, with the exception of a post hoc analysis of the different cut-off values for biochemistry markers.

Agreements and disagreements with other studies or reviews

Previous observational studies have suggested that higher folate status in pregnancy is associated with higher birthweight, higher placental weight, and prolonged gestation (Goldenberg 1992; Neggers 1997; Tamura 1992). Preconception folic acid supplementation has also shown effects on decreasing preterm births (Bukowski 2009). However, the findings from this review are inconclusive.

A review on folic acid supplementation during pregnancy by Charles et al (Charles 2005b) that included results from large randomised controlled trials found no conclusive evidence of benefit for folic acid supplementation in pregnant women. An earlier version of this Cochrane review also reached the same conclusion (Mahomed 1997).

Authors' conclusions

Implications for practice

Our meta-analysis of folic acid supplementation in pregnancy included 31 studies and provided non-conclusive evidence of folic acid supplementation for pregnant women on pregnancy outcomes except for improvement in mean birthweight. A reduction in the risk of megaloblastic anaemia and improvement in folate levels, however, has been noted with folic acid supplementation against supplementation with placebo but the limitation to this finding is the few number of studies reporting the outcome.

Implications for research

More well-designed, large scale randomised controlled trials are needed to establish the benefit of folic acid supplementation during pregnancy. Researchers of future trials should also make efforts to describe the participants in more detail before enrolment and should undertake long-term follow-up of the participants and their children in order to study the long-term effects of folic acid supplementation. Bias should also be reduced by adequate randomisation and allocation concealment of the assignment of intervention by achieving blinding of the participants, providers and the outcome assessors and by minimising loss to follow-up of the participants, in order to produce trials of adequate methodological quality.

Acknowledgements

We thank Kate Barton and Rebecca Gainey as translators of Lira 1989; Elena Intra as translator of Polatti 1992; Alison Ledward as translator of Weil 1977, Austin Anderson Leirvik as translator of Tchernia 1982 and Caroline Summers as translator of Balmelli 1974 and Roth 1980.

As part of the pre-publication editorial process, this review has been commented on by three peers (an editor and two referees who are external to the editorial team), a member of the Pregnancy and Childbirth Group's international panel of consumers and the Group's Statistical Adviser.

Data and analyses

Download statistical data

Comparison 1. Folic acid versus no folic acid
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Preterm birth32959Risk Ratio (Fixed, 95% CI)1.01 [0.73, 1.38]
1.1 As categorised by: birth between 36-38 weeks of gestation153Risk Ratio (Fixed, 95% CI)0.75 [0.33, 1.71]
1.2 As categorised by: birth before 38 weeks of gestation1109Risk Ratio (Fixed, 95% CI)0.14 [0.01, 2.65]
1.3 As categorised by: birth before 37 weeks of gestation12797Risk Ratio (Fixed, 95% CI)1.09 [0.77, 1.54]
2 Stillbirths/neonatal deaths33110Risk Ratio (M-H, Fixed, 95% CI)1.33 [0.96, 1.85]
3 Low birthweight43113Risk Ratio (M-H, Fixed, 95% CI)0.83 [0.66, 1.04]
3.1 Less than 2500 g33089Risk Ratio (M-H, Fixed, 95% CI)0.80 [0.63, 1.02]
3.2 Less than 2400 g124Risk Ratio (M-H, Fixed, 95% CI)1.3 [0.79, 2.15]
4 Mean birthweight (g)5774Mean Difference (IV, Random, 95% CI)104.96 [-25.50, 235.41]
4.1 Folate + Iron5774Mean Difference (IV, Random, 95% CI)104.96 [-25.50, 235.41]
5 Mean birth weight (sensitivity analysis-after removing Trigg 1976)4625Mean Difference (IV, Random, 95% CI)135.76 [47.85, 223.68]
5.1 Folate + Iron4625Mean Difference (IV, Random, 95% CI)135.76 [47.85, 223.68]
6 Pre-delivery anaemia84149Risk Ratio (M-H, Random, 95% CI)0.62 [0.35, 1.10]
6.1 Anaemia: as categorized by haemoglobin < 11 g/dL135Risk Ratio (M-H, Random, 95% CI)2.8 [0.39, 19.93]
6.2 Anaemia: as categorized by haemoglobin < 10.5 g/dL2407Risk Ratio (M-H, Random, 95% CI)0.70 [0.31, 1.61]
6.3 Anaemia: as categorized by haemoglobin < 10 g/dL22448Risk Ratio (M-H, Random, 95% CI)0.35 [0.05, 2.42]
6.4 Anaemia: did not mention their cut-off31259Risk Ratio (M-H, Random, 95% CI)0.71 [0.25, 2.02]
7 Mean pre-delivery haemoglobin level121806Mean Difference (IV, Random, 95% CI)-0.03 [-0.25, 0.19]
7.1 Folate + Iron121806Mean Difference (IV, Random, 95% CI)-0.03 [-0.25, 0.19]
8 Mean pre-delivery haemoglobin level121806Mean Difference (IV, Random, 95% CI)-0.03 [-0.25, 0.19]
8.1 Folic acid < 400 µg7582Mean Difference (IV, Random, 95% CI)0.06 [-0.09, 0.20]
8.2 Folic acid >400 µg51224Mean Difference (IV, Random, 95% CI)-0.17 [-0.54, 0.21]
9 Mean pre-delivery serum folate81250Std. Mean Difference (IV, Random, 95% CI)2.03 [0.80, 3.27]
9.1 Folate + Iron81250Std. Mean Difference (IV, Random, 95% CI)2.03 [0.80, 3.27]
10 Mean pre-delivery serum folate81250Std. Mean Difference (IV, Random, 95% CI)2.03 [0.80, 3.27]
10.1 Folic acid < 400 µg4253Std. Mean Difference (IV, Random, 95% CI)3.70 [0.28, 7.11]
10.2 Folic acid > 400 µg4997Std. Mean Difference (IV, Random, 95% CI)0.68 [-0.75, 2.10]
11 Low pre-delivery serum folate2696Risk Ratio (M-H, Fixed, 95% CI)0.38 [0.25, 0.59]
11.1 Pre-delivery serum folate: as categorised by < 2.5 ng/mL1643Risk Ratio (M-H, Fixed, 95% CI)0.31 [0.16, 0.63]
11.2 Pre-delivery serum folate: did not report the cut-off value153Risk Ratio (M-H, Fixed, 95% CI)0.48 [0.30, 0.78]
12 Mean red cell folate4427Std. Mean Difference (IV, Random, 95% CI)1.59 [-0.07, 3.26]
12.1 Folate + Iron4427Std. Mean Difference (IV, Random, 95% CI)1.59 [-0.07, 3.26]
13 Megaloblastic anaemia43839Risk Ratio (M-H, Fixed, 95% CI)0.21 [0.11, 0.38]
Analysis 1.1.

Comparison 1 Folic acid versus no folic acid, Outcome 1 Preterm birth.

Analysis 1.2.

Comparison 1 Folic acid versus no folic acid, Outcome 2 Stillbirths/neonatal deaths.

Analysis 1.3.

Comparison 1 Folic acid versus no folic acid, Outcome 3 Low birthweight.

Analysis 1.4.

Comparison 1 Folic acid versus no folic acid, Outcome 4 Mean birthweight (g).

Analysis 1.5.

Comparison 1 Folic acid versus no folic acid, Outcome 5 Mean birth weight (sensitivity analysis-after removing Trigg 1976).

Analysis 1.6.

Comparison 1 Folic acid versus no folic acid, Outcome 6 Pre-delivery anaemia.

Analysis 1.7.

Comparison 1 Folic acid versus no folic acid, Outcome 7 Mean pre-delivery haemoglobin level.

Analysis 1.8.

Comparison 1 Folic acid versus no folic acid, Outcome 8 Mean pre-delivery haemoglobin level.

Analysis 1.9.

Comparison 1 Folic acid versus no folic acid, Outcome 9 Mean pre-delivery serum folate.

Analysis 1.10.

Comparison 1 Folic acid versus no folic acid, Outcome 10 Mean pre-delivery serum folate.

Analysis 1.11.

Comparison 1 Folic acid versus no folic acid, Outcome 11 Low pre-delivery serum folate.

Analysis 1.12.

Comparison 1 Folic acid versus no folic acid, Outcome 12 Mean red cell folate.

Analysis 1.13.

Comparison 1 Folic acid versus no folic acid, Outcome 13 Megaloblastic anaemia.

History

Protocol first published: Issue 1, 2008
Review first published: Issue 3, 2013

DateEventDescription
16 February 2010AmendedAuthor contact details edited.
20 September 2008AmendedConverted to new review format.

Contributions of authors

Zohra Lassi entered the data, created the comparisons, conducted the analyses and wrote the text of the review under the guidance of Dr Zulfiqar Bhutta. The draft protocol was written by Dr Batool Haider (BAH) who also designed the eligibility and data extraction forms. Rehana Salam (RAS) took part in assisting with data analysis.

Declarations of interest

None known.

Sources of support

Internal sources

  • The Aga Khan University, Pakistan.

External sources

  • No sources of support supplied

Differences between protocol and review

Outcome measures have been separated into 'Primary' and 'Secondary' outcomes.

We have added two additional outcomes: respiratory disease in the child; allergic disease in the child.

Notes

This review has been developed to update the previously published review, 'Folate supplementation in pregnancy' , which was withdrawn from publication in Issue 3, 2006, of The Cochrane Library because it was out of date. See Other published versions of this review.

Characteristics of studies

Characteristics of included studies [ordered by study ID]

Balmelli 1974

MethodsIt was a RCT in which women were randomised into 2 groups and recruited from Clinic for Female Medicine at the University of Bern (Switzerland). Average age for iron group was 27.8 years while for Iron + folic acid group was 26.9 years. Measurement were taken over the period of 12 weeks. Blood samples were taken at monthly intervals.
ParticipantsPregnant women between 20-25 weeks of pregnancy (n = 42).
Interventions

Group 1: ferrous sulphate 125 mg + vitamin B12 100 µg (n = 21).

Group 2: ferrous sulphate 125 mg + folic acid 100 µg + vitamin B12 100 µg (n = 21).

OutcomesPre-delivery haemoglobin level (n = 42), serum folate level (n = 42).
NotesAll the women were the residents of Switzerland for longer than a year. Participants were restricted to patients with a haemoglobin level between 10-12 g%, suspected abnormal pregnancies or patients suffering from intercurrent illness were excluded from study.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskAdequate sequence generation was not described in the text.
Allocation concealment (selection bias)High risk

Quote " women were randomised into two groups".

Comment: probably not done.

Blinding (performance bias and detection bias)
All outcomes
High riskTreatment was not blinded.
Incomplete outcome data (attrition bias)
All outcomes
Low riskReasons for exclusion were described. Attrition (21%) with reasons were mentioned in the study.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Batu 1976

MethodsThis RCT was conducted on Burmese women. Women were randomly placed into the treatment groups. Venous blood was collected before the commencement of treatment, near full term (38th to 40th week), and 4 to 7 weeks after birth.
ParticipantsWomen attending antenatal clinic in Rangoon for their antenatal visit (n = 96).
Interventions

Group1: iron 60 mg (n = 30).

Group2: iron 60 mg+ folic acid 5 mg (n = 25).

Group3: placebo (n = 22).

Group4: folic acid 5 mg (n = 19).

OutcomesPre-delivery haemoglobin level (n = 46).
NotesFor this review we compared group 2 with group 1 and group 3 with group 4.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "women were randomly placed to one of four treatment regimens".
Allocation concealment (selection bias)Unclear riskThe methods used for allocation concealment was not stated in the text.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskBlinding was not described in the text.
Incomplete outcome data (attrition bias)
All outcomes
High riskExclusion number and reasons were not described the text, while attrition (69%) was given with reasons.
Selective reporting (reporting bias)Unclear riskInsufficient information to make any judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Baumslag 1970

MethodsThis was a randomised trial conducted on all pregnant women who were attending antenatal clinics at the Baragwanath and South Rand Hospitals, Johannesburg (South Africa). Pregnant women were allocated into 3 interventions groups based on random numbers.
ParticipantsAll pregnant women attending antenatal clinics at Baragwanath and South Rand Hospitals, Johannesburg (n = 355).
Interventions

Group 1 received 200 mg of iron by mouth (n = 115).

Group 2 received 5 mg of folic acid daily by mouth in addition to the iron (n = 127).

Group 3 received 50 µg of vitamin B12 by mouth in addition to the folic acid and iron (n = 113).

OutcomesBirthweight was measured.
Notes

Birthweight was analysed separately for Bantu participants and white participants. In the white participants supplementation was started after the 24th week, while supplementation in Bantu participants was started after 28th week.

We compared the data of group 1 with group 2 only.

Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "patients were allocated by random numbers to three groups".
Allocation concealment (selection bias)Unclear riskInsufficient information about allocation concealment.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsufficient information about blinding.
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information about exclusion and attrition.
Selective reporting (reporting bias)Low riskThe study has mentioned data on all outcome measure mentioned as objective.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Blot 1981

MethodsThis was a RCT conducted on women coming for antenatal examination in Paris. Each women was given a bottle containing iron or a combination thereof with folic acid. The 2 groups of women were totally comparable on their baseline characteristics.
ParticipantsAll women attending for the compulsory antenatal examination at the end of 6th month of pregnancy (n = 109).
Interventions

Group1: iron 105 mg (n = 55).

Group2: iron 105 mg + folic acid 350 mg (n = 54).

OutcomesPre-delivery haemoglobin levels (n = 109).
NotesAll women were given ascorbic acid 500 mg. Study population was generally from upper social class which may lead to underestimation of nutritional deficiencies.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear risk

Quote: "patients were given bottle of 90 tablets, contained either iron or the combination of iron with folic acid".

Comment: probably not done.

Allocation concealment (selection bias)Low riskBottle of tablets without the awareness of intervention type was given to patients.
Blinding (performance bias and detection bias)
All outcomes
Low riskNeither the patient nor the obstetrician was aware of the nature of treatment.
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskData on exclusion with its reason were not described in the text. Attrition (45.5%) with reasons were reported.
Selective reporting (reporting bias)Low riskStudy appears to be free of selective reporting.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Castren 1968

MethodsThis RCT was conducted on pregnant women coming to the Maternity Centre of Turku (Finland). 63 women in each groups were started on prophylactic intervention and control treatment. Blood samples were studied 3 times: first before the institution of therapy in the 10th to 20th week of pregnancy, second in the 21st to 30th week, and third at the end of pregnancy in the 31st to 40th week.
ParticipantsHealthy pregnant women who at the time of examination at the centre had shown no signs of anaemia (n = 126).
Interventions

Group 1 comprised of 63 women started on 200 mg of ferrous sulphate and (n = 63).

Group 2 was started on 200 mg of ferrous sulphate and 3 mg of folic acid (n = 63).

OutcomesPre-delivery haemoglobin level (n = 109), pre-delivery serum folate (n = 109).
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)High risk

Quote: "series of patients were collected from maternity centers of Turku and then the series was divided into two groups".

Comment: probably not done.

Allocation concealment (selection bias)Unclear riskInsufficient information about allocation concealment.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsufficient information about blinding.
Incomplete outcome data (attrition bias)
All outcomes
Low riskNumber of pregnant women excluded was not mentioned nor its reasons. Attrition (14%) was mentioned along with its reasons.
Selective reporting (reporting bias)Low riskStudy appears to be free of selective reporting.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Chanarin 1965

MethodsThe RCT was conducted on pregnant women coming to antenatal clinics at Saint Mary Hospital, London.
ParticipantsPregnant women coming to antenatal clinic (n = 144).
Interventions

Women were allocated to 1 of the following 3 groups.

Group 1: ferrous fumarate 100 mg (n = 50).

Group 2: ferrous fumarate with 10 µg folic acid (n = 52).

Group 3: lactose (n = 42).

Subjects were asked to take 1 throughout pregnancy.

OutcomesMean urinary excretion (n = 144), mean haemoglobin (n = 144).
NotesFor this review, group 1 was compared with group 2.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "women were allocated at random to one of the three groups".
Allocation concealment (selection bias)High riskInsufficient information about allocation concealment.
Blinding (performance bias and detection bias)
All outcomes
Low risk

Quote: "Glaxo Laboratories supplied these drugs with green, blue or red labels and the precise contents of each batch being unknown to us during the trials".

Comment: investigators blinded, it seem from the available information that it was a single blinded study.

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information.
Selective reporting (reporting bias)Unclear riskInsufficient information.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Chanarin 1968

MethodsThis was a RCT in which women attending the antenatal clinic at St. Mary's hospital (London) took part in the study.
Participants206 women took part in this study. They all were less than 16 weeks of pregnancy. Women were given 1 g of IV Iron dextran as 4 250 mg doses at weekly intervals. At the 20th week they were assigned in to groups (n = 206).
Interventions

Ferrous fumarate 260 mg (n = 101).

Ferrous fumarate 260 mg and 100 µg folic acid (n = 105).

OutcomesChanges in haemoglobin (n = 206), serum iron (n = 206), serum folate (n = 206) and red cell folate levels (n = 206).
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "Allotted to one of the two groups".
Allocation concealment (selection bias)Unclear riskInsufficient information to permit any judgement.
Blinding (performance bias and detection bias)
All outcomes
Unclear risk

Quote: "The survey being conducted as a blind trial".

Comment: probably not done.

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information to permit any judgment.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit any judgment.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Charles 2005

MethodsThis is a RCT in which during the period June 1966 to June 1967, women (resident of Aberdeen city, Scotland) were identified as potentially eligible to enter into this study to examine the effect of folic acid supplementation on pregnancy outcome.
ParticipantsAll pregnant women booking for antenatal care under 30 weeks' gestation (n = 2928).
Interventions

Women were assigned into 3 groups.

Group 1: folic acid 200 µg daily doses (n = 466).

Group 2: folic acid 5 mg daily doses (n = 485).

Group 3: placebo (n = 1977).

OutcomesBirthweight, placental weight, gestational age at delivery, placenta praevia, pre-eclampsia, fetal abnormality and stillbirth or neonatal deaths (n = 2819).
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "Randomised".
Allocation concealment (selection bias)High risk

Quote: "The tablets were kept in numbered drawers and distributed in sequence; during the first 2 weeks of recruitment, the tablets were not ready for distribution and 109 patients recruited at this time received no treatment ad were therefore not eligible for randomisation".

Comment: probably not done.

Blinding (performance bias and detection bias)
All outcomes
Low risk

Quote: "the study was a double blinded so neither the trial author, nor the patient knew the code to the tablets they were receiving".

Comment: probably done.

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information to permit judgement.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Chisholm 1966

MethodsWomen attending the antenatal clinic at their first visit before the 28th week of pregnancy were asked to participate in a randomised clinical trial to investigate the best method of preventing anaemia during pregnancy in Oxford (UK).
ParticipantsWomen who had haemoglobin level less than 11 g per 100 mL and serum iron of less than 60 µg per 100 mL were not included in the trial and were treated immediately (n = 542).
InterventionsHalf of the patient treated with ferrous gluconate (300 mg) 3 times daily (n = 183) and half with placebo tablets (n = 177). These groups were again divided into 3 groups; 1 group was given 500 µg (n = 61), or a high dose of 5 mg folic acid (n = 62) or a placebo (n = 59).
OutcomesMean haemoglobin level (360), red cell folate level and folate levels (360).
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "Random allocation of women to one of the 6 treatment groups".
Allocation concealment (selection bias)Unclear risk

Quote: "Bottles containing the tablets were numbered by random selection".

Comment: .insufficient information to permit judgement.

Blinding (performance bias and detection bias)
All outcomes
Unclear risk

Quote: "code was not known while the patients were still on trial".

Comment: participants were blinded.

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information to permit judgement.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Christian 2003

MethodsThe study was a cluster-randomised, double-blind trial that featured an active control group and was conducted in the rural plains district of Sarlahi, Nepal.
Participants4926 pregnant women and their 4130 infants in rural Nepal.
Interventions

In addition to vitamin A (1000 g retinol equivalents), the intervention groups received either:

  • folic acid (FA; 400 g), (n = 941)

  • FA + iron (60 mg), (n = 957)

  • FA + iron + zinc (30 mg), (n = 999) or

  • Multiple micronutrients (MNs; the foregoing plus 10 g vitamin D, 10 mg vitamin E, 1.6 mg thiamine, 1.8 mg riboflavin, 2.2 mg vitamin B-6, 2.6 g vitamin B-12, 100 mg vitamin C, 64 g vitamin K, 20 mg niacin, 2 mg Cu, and 100 mg Mg) (n = 1050).

The control group received vitamin A only (n = 1051).

OutcomesPerinatal deaths, Infant deaths, neonatal deaths.
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Low risk

Quote: "Randomization was done in blocks of 5 within each village development community by the senior study investigators, who drew numbered chips from a hat."

Comment: Probably done.

Allocation concealment (selection bias)Low risk

Quote: "The supplements, which were of identical shape, size, and color, arrived in Nepal in opaque, sealed, and labelled bottles coded 1–5. The code allocation was kept locked at the Johns Hopkins University, Baltimore."

Comment: Probably done.

Blinding (performance bias and detection bias)
All outcomes
Low riskQuote: "The investigators, field staff, and participants were blinded to the codes throughout the study."
Incomplete outcome data (attrition bias)
All outcomes
Low risk< 0.5% in all arms combined.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Dawson 1962

MethodsPatients attending antenatal clinic were selected for this RCT in Crumpsall Hospital, Manchester.
ParticipantsWomen attending antenatal clinic and were at or before 28 weeks of pregnancy were selected (n = 144).
InterventionsWomen were assigned to receive intervention (folic acid 15 mg ) (n = 63) or control group (n = 81).
OutcomesPrepartum and postpartum haemoglobin levels.
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)High risk

Quote: "Women were allotted a group in order in which they were booked".

Comment: probably not done.

Allocation concealment (selection bias)Unclear riskInsufficient information to permit judgment.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsufficient information to permit judgment.
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information to permit judgment.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgment.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Decsi 2005

MethodsThis is a placebo-controlled, randomised, double-blind trial on expecting mothers living in Germany, Hungary and Spain.
ParticipantsExpectant women from the 20th week of gestation (n = 312).
Interventions

Women received either:

Group A: 500 mg Docosahexaenoic Acid (DHA) (n = 77)

Group B: or 400 mg Methyltetrahydofolate (5-MTHF) (n = 80)

Group C: or placebo (n = 80)

Group D: or the combination of 500 mg DHA and 400 mg 5-MTHF (n = 75).

OutcomesContribution of docosahexaenoic acid (DHA) to the fatty acids of erythrocyte phophatidylcholine (PC) and phosphatidylethanolamine (PE) lipids at delivery (n = 312).
NotesFor this review, we compared group B with group C. and group A with group D.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear risk

Quote: "....randomized,..."

Comment: insufficient information to permit judgment.

Allocation concealment (selection bias)Unclear riskInsufficient information to permit judgment.
Blinding (performance bias and detection bias)
All outcomes
Low riskQuote: "....double blind,..."
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information to permit judgment.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgment.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Edelstein 1968

MethodsPatients were Bantu (Johannesberg, South Africa) attending Baragwanath Hospital were randomly allocated to 1 of the 2 groups in this RCT.
ParticipantsPregnant women (n = 396).
Interventions

Group1: iron 200 mg (n = 235).

Group 2: iron 200 mg + folic acid 5 mg (n = 89).

Group3: iron 200 mg, folic acid 5 mg + vit B12 50 µg (n = 72).

OutcomesPre-delivery haemoglobin levels (n = 172), postpartum haemoglobin levels (n = 291), pre-delivery folate levels (n = 211), postpartum folate levels (n = 291).
NotesTheir diet largely contains maize. For this review we only compared group 1 with group 2.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "pregnant patients were randomly allocated to one of the two groups".
Allocation concealment (selection bias)Low riskAll tables were dispensed at identical gelatin capsules.
Blinding (performance bias and detection bias)
All outcomes
Low riskThe type of supplementation was not known to the participants or the laboratory staff.
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskExclusion and attrition (or reasons) were not reported.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Fleming 1968

MethodsThe RCT was conducted in Nigeria. Alternate women were allotted to 2 groups in the order in which they attended the clinic.
ParticipantsWomen with primigravida less than 26 weeks' pregnant with PCV 27% or more, and who had not received any treatment (n = 53).
InterventionsGroup 1: lactose based tab (n = 26), group 2: folic acid 5 mg (n = 27).
OutcomesPremature births (n = 53), folate deficiency (n = 53).
NotesAll the women received antimalarials and iron supplements.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)High risk

Quote: "alternate patients were allotted to group A or group B in the order in which they attended the clinic".

Comment: probably not done.

Allocation concealment (selection bias)Low riskTablets for both the groups were coloured in the same manner.
Blinding (performance bias and detection bias)
All outcomes
Low riskThe identity of the tablets was not known to investigators until after the completion of the trial.
Incomplete outcome data (attrition bias)
All outcomes
Low riskNumber of exclusions were not mentioned (nor the reasons). Numbers of attrition (28%) were described but their reasons were not given in the text.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Fletcher 1971

MethodsThis RCT was conducted on the women living in London. Participants were ascribed at random to 2 treatment groups.
ParticipantsPregnant women booked for antenatal clinic (n = 643).
Interventions

Group1: ferrous sulphate 200 mg (n = 322).

Group 2: ferrous sulphate 200 mg + folic acid 5 mg (n = 321).

OutcomesPre-eclampsia (n = 643), serum folate levels (n = 643).
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "the subjects were ascribed at random to two treatment groups by instructing each patient to take one tablet daily".
Allocation concealment (selection bias)Unclear riskThe methods used for allocation concealment was not stated in the text.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskThe methods used for blinding was not stated in the text.
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskNumber of exclusions and attritions (along with their reasons) were not reported.
Selective reporting (reporting bias)Unclear riskThe study appears to be free of selective reporting.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Giles 1971

MethodsDouble-blind controlled trial conducted on patients coming for their antenatal visits at Royal Women's Hospital, Melbourne. Women were allotted to the groups based on the order they were presented. Loss to follow-up was between 10% to 20%.
ParticipantsPregnant women (n = 620).
Interventions

Group 1 (folic acid - Tiger) ferrous sulphate 200 mg (n = 308).

Group 2 (folic acid - Lion) folic acid 5 mg (n = 312).

OutcomesLow pre-delivery anaemia (n = 620), birthweight (n = 620), neonatal deaths (n = 620).
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)High risk

Quote: "members of each group were numbered consequently in the order in which they presented".

Comment: probably not done.

Allocation concealment (selection bias)Low risk

Quote: "the pharmacist, after consulting a list of random numbers, dispensed either folic acid-tiger or folic acid-lion from the two large stock bottles. these tablets looked identical, and the dispensing pharmacist did not know which was the placebo".

Comment: probably done.

Blinding (performance bias and detection bias)
All outcomes
Low risk

Quote: "a double-blind control trial".

Comment: probably done.

Incomplete outcome data (attrition bias)
All outcomes
Low riskExclusion data with their reasons were not reported in the study. Attrition (15%) along with reasons were reported.
Selective reporting (reporting bias)Unclear riskThe study appears to be free of selective reporting.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Harrison 1985

MethodsDouble-blind study. The identity of the tables was not known to researcher before the analysis of the study data and women were randomised to 1 of the 5 groups. Conducted in Nigeria.
ParticipantsPregnant women of 8 to 24 weeks of pregnancy (n = 69).
Interventions

Group A: placebo only (n = 10).

Group B: single dose of chloroquine 600 mg and followed by prognamil 100 mg (n = 18).

Group C: ferrous sulphate 60 mg (n = 12).

Group D: folic acid 1 mg (n = 10).

Group E: ferrous sulphate 60 mg + folic acid 1 mg (n = 9).

OutcomesRed cell folate (µg/L) levels, serum folate levels (n = 69).
NotesFor this review group E was compared with group A.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "women were randomised in different treatment groups".
Allocation concealment (selection bias)Unclear riskThe methods used for allocation concealment was not given in the text.
Blinding (performance bias and detection bias)
All outcomes
Low riskQuote: "the medication was double blind, the identity if the tablets not being known to the researchers before the analysis of the data".
Incomplete outcome data (attrition bias)
All outcomes
Low riskExclusion and attrition were mentioned together (70%) along with their reasons.
Selective reporting (reporting bias)Low riskThe study has mentioned data on all outcome measures mentioned as objectives.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Hibbard 1969a

MethodsThis was a triple-blind study conducted in Mill Road, maternity hospital, Liverpool, UK. The patients were divided into three groups.
ParticipantsPregnant women (before 20 weeks) with defective folate metabolism and excessive FIGLU excretion or low serum folate level (< 2 ng/mL) were admitted in the trial (n = 69).
InterventionsTreatment groups were daily folic acid 500 µg (n = 27), 0.5 mg folic acid (n = 26), and placebo (n = 26).
OutcomesSerum folate levels and severe anaemia.
NotesEach group received 60 elemental iron within the trial medicine.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "Patients were divided into three groups"
Allocation concealment (selection bias)Unclear risk

Quote" patients were allocated in consecutive numbers" ; "code was not known whilst the trial was in progress"

Comment: Not enough information to permit judgement.

Blinding (performance bias and detection bias)
All outcomes
Low riskQuote: "...gelatin coated capsule of identical appearance..."
Incomplete outcome data (attrition bias)
All outcomes
Low riskApproximately 19% were lost to follow-up and folate levels were also checked in the final non-attendees.
Selective reporting (reporting bias)Low riskThe study has reported data on outcome measures mentioned as objectives.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Iyengar 1975

MethodsThis RCT was conducted in Niloufer Hospital, Hyderabad (India). Women were alternatively assigned to treatment groups. Groups were matched on parity and height. The women were followed at monthly intervals until 32 weeks of gestation, once every 2 weeks until 36 weeks, and at weekly intervals thereafter until delivery.
ParticipantsPregnant women between 20 and 28 weeks of gestation (n = 288).
InterventionsGroup 1: no supplement (n = 52), Group 1: iron 60 mg (n = 96), Group 2: iron 60 mg + folic acid 500 µg (n = 134).
OutcomesBirthweight (n = 230).
NotesPregant women belonging to low income less than Rs. 3000/- per month.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)High risk

Quote: "alternate subjects received either of therapy".

Comment: probably not done.

Allocation concealment (selection bias)Unclear riskInsufficient information to permit judgement regarding allocation concealment.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsufficient information to permit judgement regarding blinding.
Incomplete outcome data (attrition bias)
All outcomes
Low riskExclusion data with their reasons were not reported in the study. Attrition (> 20%) along with reasons were reported.
Selective reporting (reporting bias)Low riskStudy seems to be free from selective reporting.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Lira 1989

MethodsThis is a RCT in which all pregnant women attending the outpatient obstetrics clinic at the Catholic University’s Clinical Hospital (Chile).
ParticipantsWomen with less than 16 weeks of pregnancy were selected (n = 153).
InterventionsTreatment group received a preparation containing equal quantities of iron and folic acid, 350 µg (plus 500 mg of ascorbic acid) (n =78 and 75).
OutcomesHaemoglobin (g/dL), haematocrit (%), serum iron (µg/dL), transferrin (µg/dL), transferrin saturation (%), serum folate (ng/mL), red cell folate (ng/mL), plasmatic volume (mL) (n = 153).
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "Women were divided into 2 groups randomly".
Allocation concealment (selection bias)Unclear riskInsufficient information to permit judgement.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsufficient information to permit judgement.
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information to permit judgement.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Menon 1962

MethodsThis is a RCT conducted in Inida, in which women were allotted to each group in the order they were registered.
ParticipantsPregnant women between 16 weeks and 24 weeks whose haemoglobin level was at or above 10.5 gm% (14.5 gm = 100%) (n = 273).
Interventions

Group 1 was given 5 g of ferrous sulphate (n = 88).

Group 2 was given 5 mg of folic acid (n = 90).

Group 3 was given 5 g of ferrous sulphate and 5 mg of folic acid (n = 90).

OutcomesFall in pre-delivery haemoglobin level (n = 273).
NotesAll the women were given multivitamin along with these treatments. In this review we compared group 1 with group 3.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)High risk

Quote: "subjects were allotted to each group in the order in which they registered".

Comment: probably not done.

Allocation concealment (selection bias)Unclear riskInsuffient information on allocation concealment.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsuffient information to make any judgment regarding blinding.
Incomplete outcome data (attrition bias)
All outcomes
Low riskExclusion data with their reasons were not reported in the study. Attrition (> 20%) along with the reasons were reported.
Selective reporting (reporting bias)Low riskStudy seemed to be free from selective reporting.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Metz 1965

MethodsThis RCT was conducted at the antenatal clinic at South Rand Hospital, Johannesburg, South Africa.
ParticipantsA total of I75 pregnant white women attending the clinics were selected.
Interventions

Group 1: 200 mg of iron orally daily, either as ferrous sulphate or ferrous fumarate (n = 57).

Group 2 iron as in group 1 together with 5 mg of folic acid orally daily (n = 60).

Group 3 vitamin B12 orally (daily in addition to iron and folic acid as in group 2 (n = 58).

OutcomesUrinaru FIGLU (n = 175), serum folate activity, serum vitamin B12 concentration, serum haemoglobin and haematocrit (n = 175).
NotesIn this review group 1 was compared with group 2.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "patients were randomly allocated to one of three groups...".
Allocation concealment (selection bias)Unclear riskInsufficient information to permit judgement.
Blinding (performance bias and detection bias)
All outcomes
Unclear risk

Quote: "All tablets were dispensed in identical gelatin capsules".

Comment: insufficient information to permit judgement.

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information to permit judgement.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Pack 1980

MethodsThis is a double-blind study from NewZealand.
ParticipantsPregnant women in 4th and 8th months of gestation were enrolled (n = 30).
Interventions

Group A: received placebo mouth wash and tablets (n = 10).

Group B: received placebo mouth wash and 5 mg folate tablets (n = 10).

Group C: folic acid mouth wash and placebo tablets (n = 10).

OutcomesCorrelation between gingival index and plaque index (n = 30).
NotesIn this review, we compared group B with group A.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear risk

Quote: "thirty women were randomly divided in 3 roups of 10".

Comment: insufficient information on sequence generation.

Allocation concealment (selection bias)Unclear riskInsuffient information on allocation concealment.
Blinding (performance bias and detection bias)
All outcomes
Low risk

Quote: "double blind".

Comment: probably done.

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsuffient information on outcome data.
Selective reporting (reporting bias)Unclear riskInsuffient information to make any judgment.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Rae 1970

MethodsThis was a RCT. Randomisation was done according to a day of week on which women coming for antenatal clinic in Liverpool (UK). Samples of venous blood were taken from patients in both groups at the first visit to the antenatal clinic, at the 32nd and 36th weeks of pregnancy, and during the first 3 days of puerperium.
ParticipantsPregnant women coming for antenatal visits (n = 698).
InterventionsPregnant women coming on Monday was assigned were prescribed ferrous gluconate 200 mg, while those coming in Tuesday were given same dose of ferrous gluconate in addition to a folic acid 5 mg. Monday group (n = 463) and Tuesday group (n = 235), total (n = 698).
OutcomesLow pre-delivery anaemia (< 10.9 g/dL) (n = 698), megaloblastic anaemia (n = 698).
NotesPatients with a haemoglobin concentration of 10.9 g/dL or more were classified 'not anaemic', and those with a haemoglobin concentration of under 10.9 g/dL were classified 'normoblastic' or 'megaloblastic' according to the marrow smear.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)High risk

Quote: "patients were allocated at random to one or other of the two groups, depending on which day of the week they attended the antenatal clinic".

Comment: probably not done.

Allocation concealment (selection bias)Unclear riskInsufficient information to permit judgement.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsufficient information to permit judgement.
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information to permit judgement.
Selective reporting (reporting bias)Low riskThe study has mentioned data on all outcome measures mentioned as objectives.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Rolschau 1979

MethodsThis was a controlled trial conducted on women attending antenatal clinic of Odense University Hopsital. The criteria for selecting women was Danish birth and a normal pregnancy. Women were matched on parity, tobacco consumption, pre-pregnant weight, housing condition and age.
ParticipantsPregnant women in 21 to 25 week of gestation (n = 36).
InterventionsGroup1: iron 250 mg (n = 16), group 2: iron 250 mg + folic acid 5 mg (n = 20).
OutcomesBirthweight.
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "Subjects were allotted to two groups".
Allocation concealment (selection bias)Low risk

Quote: 'groups were supplied similar tablets".

Comment: probably done.

Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsufficient information to make any judgement.
Incomplete outcome data (attrition bias)
All outcomes
Low riskNumber excluded nor its reasons mentioned. Attrition (10%) was reported but reasons were not described.
Selective reporting (reporting bias)Unclear riskInsufficient information to make any judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Roth 1980

MethodsThis is a RCT conducted during August 1976 - September 1977.
Participants23 pregnant women were selected.
Interventions

Group A (11 patients): 1 x Tardyferon-Fol tablet per day (80 mg iron sulphate, 80 mg mucoproteose, 350 µg folic acid) during pregnancy.

Group B (12 patients): 1 x Tardyferon tablet per day (80 mg iron sulphate, 80 mg mucoproteose, no folic acid content) during pregnancy.

Group A: 5 dropouts.

Group B: 3 dropouts.

Reasons for dropouts included irregular intake of the medication (3), change of residence (2), premature birth (2) and 1 unexplained failure to attend the final check-up.

OutcomesHaemoglobin level, red cell folate levels and serum folate levels (n = 23).
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear risk

Quote: "Randomised".

Comment: insufficient information to make any judgement.

Allocation concealment (selection bias)Unclear risk

Quote: "The tablets used in treatment were identical in appearance".

Comment: insufficient information to make any judgement.

Blinding (performance bias and detection bias)
All outcomes
Unclear risk

Quote: "Yes".

Comment: insufficient information to make any judgement.

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information to make any judgement.
Selective reporting (reporting bias)Unclear riskInsufficient information to make any judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Srisupandit 1983

MethodsThis is a RCT in which women were allocated using random number table.
ParticipantsPregnant women attending antenatal clinic of Siraj hospital Thailand (n = 329).
InterventionsGroup1: iron 60 mg (n = 109), Group 2: iron 180 mg (n = 117), Group 3: iron 180 mg + folic acid 5 mg (n = 103).
OutcomesPre-delivery haemoglobin level, serum folate levels, red cell folate levels.
NotesFor this review we compared group 2 with group 3.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Low risk

Quote: "subjects were allocated supplementation by using random table and divided into three groups".

Comment: probably done.

Allocation concealment (selection bias)Unclear riskInsufficient information to permit judgement.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsufficient information to permit judgement.
Incomplete outcome data (attrition bias)
All outcomes
Low riskExclusion and attrition were reported in a single figure (18%) with their reasons.
Selective reporting (reporting bias)Low riskThe study seems to be free from selective reporting.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Tchernia 1982

MethodsThis is a RCT on pregnant women attending the antenatal clinic and obstetric department of a hospital located in the outskirts of Paris.
ParticipantsPregnant women (n = 200).
InterventionsGroup 1: 105 mg iron (n = 100), group 2: 105 mg iron + folic acid 350 µg (n = 100).
OutcomesBirthweight, birth defects (n = 200).
Notes3 studies conducted in the actual trial, we for this review only focused on above mentioned intervention.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "women selected at random".
Allocation concealment (selection bias)Unclear riskInsufficient information to permit judgement.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsufficient information to permit judgement.
Incomplete outcome data (attrition bias)
All outcomes
Low riskNumber excluded not reported nor its reason. Reasons for attrition (> 20%) were not reported.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Trigg 1976

MethodsIt was a controlled trial conducted in London.
ParticipantsPregnant women (n = 158).
Interventions

Group 1: ferrous sulphate 50 mg (n = 76 women).

Group 2: ferrous sulphate 50 mg + folic acid 0.05 mg (n = 82 women).

OutcomesPre-delivery haemoglobin level, pre-delivery serum folate level (ng/mL), serum folate level (ng/mL), birthweight (n = 158).
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskQuote: "patients were randomly allocated to one of the two treatments".
Allocation concealment (selection bias)Unclear riskInsufficient information about the allocation concealment.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsufficient information about the blinding.
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskInsufficient information about the exclusion and attrition.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit any judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Weil 1977

MethodsDouble-blind trial, patients were randomly allocated in 2 groups. Initially 31 patients were recruited in the trial, but during the trial 1 participant from each group was excluded.
ParticipantsPregnant women of 20 weeks of gestation who were attending clinic affiliated to University of Basel, Switzerland (n = 29).
InterventionsGroup 1: ferrous sulphate 80 mg (n = 15), group 2: ferrous sulphate 80 mg + folic acid 350 µg (n = 14).
OutcomesPre-delivery haemoglobin levels (n = 29).
NotesWomen who were already taking multi-vitamin containing folic acid prior to commencement of trial were excluded.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskPatients were randomised and divided into 2 groups.
Allocation concealment (selection bias)Unclear riskInsufficient information to permit judgement.
Blinding (performance bias and detection bias)
All outcomes
Low riskDouble-blinded.
Incomplete outcome data (attrition bias)
All outcomes
Low riskNumber excluded were not reported while their reasons were described. Attrition (6%) was reported but reasons were not given.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit judgement.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Willoughby 1967

  1. a

    FIGLU: formiminoglutamic acid
    IV: intravenous
    PCV: packed cell volume
    RCT: randomised controlled trial

MethodsFor a period of 2 years (August 1964 to August 1966) every patient attending the antenatal clinic was randomly allocated to one of 5 prophylactic treatment groups in this RCT which was conducted in Glasgow (Scotland).
ParticipantsPregnant women attending clinic for antenatal visit (n = 3599).
Interventions

Group 1: iron (mg/day) = 0, folic acid (µg/day) = 0 (n = 706).

Group 2: iron (mg/day) = 105, folic acid (µg/day) = 0 (n = 736).

Group 3: iron (mg/day) = 105, folic acid (µg/day) = 100 (n = 716).

Group 4: iron (mg/day) = 105, folic acid (µg/day) = 300 (n = 715).

Group 5: iron (mg/day) = 105, folic acid (µg/day) = 450 (n = 726).

OutcomesPre-delivery anaemia (n = 3599), megaloblastic anaemia (n = 3599).
NotesPatients with haemoglobin levels below 10 g/dL at their first attendance were excluded from the trial. We compared group 3, 4 and 5 with group 2.
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)High risk

Quote: " patients attending the antenatal clinic were randomly allocated one of the five prophylactic groups".

Comment: probably not done.

Allocation concealment (selection bias)Unclear riskInsufficient information about allocation concealment.
Blinding (performance bias and detection bias)
All outcomes
Unclear riskInsufficient information about blinding.
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskNumber of pregnant women excluded and attrition rate (n = 0) were not mentioned nor their reasons.
Selective reporting (reporting bias)Unclear riskInsufficient information to permit any judgment.
Other biasUnclear riskNo other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.

Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion
Bjerre 1967Folic acid was supplemented in combination with other micronutrients versus placebo.
Colman 1974Study was to assess efficacy of folic acid supplementation in the form of food fortification.
Colman 1975Study was to assess efficacy of folic acid supplementation in the form of food fortification.
Ellison 2004Both the intervention and control group received folic acid supplementation, and groups were compared on duration of folic acid therapy. One group was given supplementation till 16 weeks of pregnancy and the other group received it till end of pregnancy.
Giles 1960There was no randomisation and intervention participants were compared with historical controls.
Gregory 2001Folate in pregnant women was compared with non-pregnant controls.
Hague 1998Published abstract of a protocol, however, study was abandoned without completion.
Hamilton 1973Nothing has been mentioned about randomisation nor the word is used. It seems this is not a randomised controlled trial.
Hekmatdoost 2011This study compares 1: 5 methyltetrahydrofolate with folic acid.
Hibbard 1969Folic acid 1.5 mg was compared with folic acid 15 mg.
Khanna 1977Included patients were already receiving iron and then therapeutic folic acid was added among women who were found to have anaemia.
Klinger 2006Effect on folic acid on placental apoptosis was assessed.
Kristoffersen 1979Only a published abstract with insufficient information was available.
Ma 2008Folic acid and iron was given along with retinol and riboflavin.
Manizheh 2009High-dose of folate was compared with low-dose folate.
Melli 2008Onlt published abstract with insufficient information was available.
Ouma 2006Association of folic acid supplementation and sulfadoxine pyrimethamine was observed.
Polatti 1992Both the intervention and control groups received folic acid supplementation. Assessed the effectiveness of folic acid when given from 12 week of pregnancy compared with given from 20 weeks of pregnancy.
Taylor 1979Experimental group was given Iron and folate and were compared with no therapy group.
Taylor 1981Experimental group was given Iron and folate and were compared with no therapy group.
Tchernia 1982aIn this paper they have reviewed and re-analysed the results of 3 different trials.
Thomson 1982Published abstract with insufficient information was only available.
Ulrich 1999Half of the participants were selected and allotted to the group based on randomisation, while other half of the study population was selected from the hospitals who delivered during the study period. Effect of folic acid was observed on development of congential anomalies.
Wang 2012This study compares folic acid, iron-folic acid or multi-micronutrients. Effect of folic acid alone cannot be determined.
Zeng 2008Both the intervention and control group were given folic acid and the intervention group also received iron.

Characteristics of ongoing studies [ordered by study ID]

Wen 2012

Trial name or titleHigh dose folic acid supplementation throughout pregnancy for pre-eclampsia prevention (FACT)
MethodsDouble blind (participant, caregiver, investigator, outcomes assessor) randomised intervention trial with parallel assignment at Ottawa Hospital Research Institute
ParticipantsPregnant women at high risk of developing pre-eclampsia
InterventionsFolic acid 4 mg, folic acid 1.0 mg x 4 tablets will be taken daily by oral administration. The majority of women in the study will routinely take 1.0 mg folic acid in a prenatal vitamin supplement, as recommended by their primary obstetrical provider; the study requirements do not require that participants change their practice. Therefore the actual total daily dose may be up to 5.1 mg of folic acid
OutcomesPre-eclampsia, Preterm birth, Stillbirth, Abortion
Starting dateApril 2011
Contact informationContact: Mark Walker, MD; Contact: Shi Wu Wen, PhD
NotesRecruiting

Ancillary