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Different types of dietary advice for women with gestational diabetes mellitus

  1. Shanshan Han1,*,
  2. Caroline A Crowther2,
  3. Philippa Middleton1,
  4. Emer Heatley2

Editorial Group: Cochrane Pregnancy and Childbirth Group

Published Online: 28 MAR 2013

Assessed as up-to-date: 16 OCT 2012

DOI: 10.1002/14651858.CD009275.pub2


How to Cite

Han S, Crowther CA, Middleton P, Heatley E. Different types of dietary advice for women with gestational diabetes mellitus. Cochrane Database of Systematic Reviews 2013, Issue 3. Art. No.: CD009275. DOI: 10.1002/14651858.CD009275.pub2.

Author Information

  1. 1

    The University of Adelaide, ARCH: Australian Research Centre for Health of Women and Babies, The Robinson Institute, Discipline of Obstetrics and Gynaecology, Adelaide, South Australia, Australia

  2. 2

    The University of Adelaide, ARCH: Australian Research Centre for Health of Women and Babies, Discipline of Obstetrics and Gynaecology, Adelaide, South Australia, Australia

*Shanshan Han, ARCH: Australian Research Centre for Health of Women and Babies, The Robinson Institute, Discipline of Obstetrics and Gynaecology, The University of Adelaide, Women's and Children's Hospital, 72 King William Road, Adelaide, South Australia, 5006, Australia. shan.han@adelaide.edu.au.

Publication History

  1. Publication Status: New
  2. Published Online: 28 MAR 2013

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Characteristics of included studies [ordered by study ID]
Balas-Nakash 2010

MethodsRandomised controlled trial.


ParticipantsN = 37 (a total of 69 women were involved in the study, but only 37 women were diagnosed with GDM and provided outcome data for this review).

Women of ≤ 30 weeks' gestation, diagnosed with Type A2 GDM (see notes), who were planning to give birth at the NIPerIER and who required medical treatment from the Department of Endocrinology at NIPerIER.

Exclusion criteria: women with T1DM, Type A1 GDM (see notes), glucose intolerance, multiple pregnancies, kidney or liver disease and hyper or hypothyroidism.

Setting: Mexico.


InterventionsLow-to-moderate GI diet group (n = 19): only foods with a low-to-moderate GI were recommended.

Control group (n = 18): any type of carbohydrate was permitted.

All women:

  1. received medical nutrition therapy from a nutritionist and diabetes educator, which included a complete evaluation of nutritional status, nutritional intervention based on a moderate restriction of calorie (24 kcal/kg) and carbohydrate (40% to 45%) intake;
  2. weight, weight gain, glycaemic control and initiation of or any alteration to insulin treatment were evaluated in each consultation;
  3. received a glucose meter and a finger prick device; frequent capillary glucose self-monitoring (6 times a day) as an intense educational component;
  4. were informed about the importance of measuring their glucose levels, how to use the glucose meter and about the recording of capillary glucose readings.


OutcomesAdherence to dietary intervention, diet intake, weight change, insulin use.


Notes
  1. No GDM diagnostic criteria reported.
  2. Type A1 GDM: abnormal OGTT but normal BGLs during fasting and 2 hours after meals; diet modification is sufficient to control glucose levels.
  3. Type A2 GDM: abnormal OGTT compounded by abnormal glucose levels during fasting and/or after meals; additional therapy with insulin or other medications is required.


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskDescribed as "women included in this study were randomly divided into two study groups", no further information available.

Allocation concealment (selection bias)Unclear riskNo information was given on allocation concealment.

Blinding of participants and personnel (performance bias)
All outcomes
High riskIt is not feasible to blind study participants due to the nature of behavioural intervention. No information on whether research personnel were blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNo information about whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes
High riskOf the total randomised cohort of 108 eligible women (mixed cohort of women with GDM and T2DM) in a clinical trial, 20 declined (15.8%) to participate in the current trial with reasons unclear. Another 19 women (17.5%) were excluded due to incomplete dietary information. No information was available for these excluded participants.

Selective reporting (reporting bias)High riskMost of the prespecified review outcomes were not reported in this trial.

Other biasLow riskNo obvious risk of other bias.

Cypryk 2007

MethodsRandomised controlled trial.


ParticipantsN = 30.

Caucasian women with newly diagnosed GDM according to WHO criteria (see notes).

Exclusion criteria not reported.

Setting: Poland.


InterventionsLow-carbohydrate diet group (n = 15): daily total energy divided as carbohydrate:45%, protein: 25%, fat: 30% (based on daily total energy of 1800 Kcal). Women were encouraged to have the diet until birth.

High-carbohydrate diet group (n = 15): daily total energy divided as carbohydrate: 60%, protein: 25%, fat: 15% (based on daily total energy of 1800 Kcal). Women were encouraged to have the diet until birth.

All women:

  1. before dietary intervention,  BGL were recorded from the patients’ diaries 3 to 4 days before study intervention;
  2. during the first 14 days after the start of interventions, women were asked to HBGM 4 times a day (fasting and 2 hours after breakfast, lunch and dinner); results were recorded in the HBGM diary;
  3. on day 15, compliance to nutritional recommendations was assessed, diary reviewed;
  4. urine ketones were checked daily.


OutcomesObstetric outcomes, BGL, intervention compliance, side-effects of the diet intervention.


NotesGDM diagnosis based on WHO criteria:

  • fasting BGL ≥ 7.0 mmol/L;
  • 2-hour BGL after 75 g glucose load ≥ 7.8 mmol/L;
  • 1 or more value(s) is (are) met or exceeded.


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskDescribed as "the patients were randomised into two groups", no further details available.

Allocation concealment (selection bias)Unclear riskNo information was given on allocation concealment.

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskIt was not feasible to blind study participants. No information on whether research personnel were blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNo information about whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes
Low riskNo loss to follow-up or post randomisation exclusion.

Selective reporting (reporting bias)High riskMost of the prespecified review outcomes were not reported in this trial.

Other biasLow riskNo obvious risk of other bias.

Grant 2011

MethodsRandomised controlled trial.


ParticipantsN = 29

Pregnant women aged at 18 to 45 years, diagnosed with GDM according to CDA criteria, and who had been referred to the Diabetes in Pregnancy Clinic (DIP), St.Michael’s Hospital, Canada.

Exclusion criteria: presence of a multiple pregnancy or an acute or chronic illness affecting carbohydrate metabolism; presence of type 1 or type 2 diabetes prior to the current pregnancy; use of insulin treatment prior to providing consent; greater than 34 weeks' gestation; and unable to communicate in English with no translator available.

Setting: Canada.


InterventionsLow-GI diet group (n = 13): participants were asked to select their starch choices from an exchange list of low-GI foods.

Intermediate or high-GI diet group (n = 16): participants were asked to select their starch choices from an exchange list of intermediate- and high-GI foods, reflecting the usual intake of typical DIP clinic patients.

All women:

  1. standard Medical nutrition therapy: patients were introduced to the Diabetes Food Guide and Canadian dietary recommendations to support a healthy pregnancy. Clinic dietitian recommended how many starch choices/ servings each participant should consume at each mean based upon their own individual gestational energy requirements and Acceptable Macronutrient Distribution Ranges;
  2. provision of approximately $20/week worth of non-perishable study foods and all blood testing strips;
  3. self-monitored blood glucose from baseline to week 8: 4 times a day (fasting, 2-h after breakfast, lunch and dinner);
  4. insulin therapy if self-monitored blood glucose were not met with lifestyle modification within 2 to 3 weeks.


OutcomesPrimary outcomes: fasting serum glucose and HbA1c at baseline and 4 weeks after intervention; SMBG from baseline to week 8.

Secondary outcomes: serum glucose, insulin, lipids and C-reactive protein at baseline and 4 weeks after intervention, maternal dietary intake, physical activity (time, type and duration), birthweight, use of insulin, macrosomia (birthweight ≥ 4000 g), LGA (> 90th percentile population specific), SGA (< 10th percentile population specific).


NotesCDA criteria used for GDM diagnosis:

  • fasting: 5.3 mmol/L;
  • 1-h 75-g OGTT: 10.6 mmol/L;
  • 2-h 75-g OGTT: 8.9mmol/L;
  • GDM: 2 of the values are met or exceeded.


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskRandomisation order was created by one of the investigators who was not involved in recruitment. It is unclear how the sequence was generated, but it is likely to be a computer-generated sequence.

Allocation concealment (selection bias)Low riskSealed, numbered, opaque envelopes were used, and various block sizes in randomisation were used.

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskDescribed as an "open-label" pilot study.

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNo information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes
Low risk3 women (10.3%) in the low-GI group withdrew after randomisation, reasons given. Data were analysed on an intent-to-treat basis.

Selective reporting (reporting bias)High riskOnly limited data were reported on some of the prespecified review outcomes.

Other biasLow riskThere is no obvious risk of other bias.

Lauszus 2001

MethodsRandomised controlled trial.


ParticipantsN = 27.

Women with a positive 3-hour 75 g OGTT before the 34 weeks' gestation.

Exclusion criteria: use of any hypoglycaemic, anti-lipidaemic or antihypertensive medication.


InterventionsHigh-carbohydrate diet group (n = 14): from 34 weeks' gestation women had a high carbohydrate diet, no details about high carbohydrate diet.

High-monounsaturated fat diet group (n = 13): from 34 weeks' gestation women had a high-monounsaturated fat diet, no details about high-monounsaturated fat diet.

All women: after being diagnosed with GDM, all women were instructed to follow a high-carbohydrate diet until the 34th week.


OutcomesPre-eclampsia, glycaemic control, insulin sensitivity, gestational weight change, maternal postpartum BMI, macrosomia, LGA, birthweight, gestational age at birth, postpartum development of diabetes mellitus.


NotesGDM diagnosis based on 3-h 75 grams OGTT, bloods taken every 30 min; GDM was defined as 2 or more plasma glucose samples above three standard deviations of the mean.


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskReported as “the randomisation was performed block-wise stratified for pre-pregnancy weight with an expected ratio of obese to normal weight of three to one.The block sizes were six and two in the two strata”.

Allocation concealment (selection bias)Low riskReported as that “the randomisation was performed by a third person at an independent centre outside our institution, which produced information about the outcome of randomisation at baseline measurement in week 33”.

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskIt was not feasible to blind study participants. No information on whether research personnel were blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNo information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes
Low riskData were missing at multiple collection points for 1 to 2 patients but this was explained in the text and is unlikely to affect the results for perinatal outcomes.

Selective reporting (reporting bias)High riskMost of the prespecified review outcomes were not reported in this trial.

Other biasHigh riskWomen in the high-monounsaturated fat diet group had a higher trial entry BMI (mean [SD]: 35 [2.4] kg/m2 ) when compared with women in the high-carbohydrate group (mean [SD]: 32.2 [1.5] kg/m2).

Louie 2011

MethodsRandomised controlled trial.


ParticipantsN = 92.

Women aged at 18–45 years, diagnosed with GDM by a 75 g OGTT between 20 and 32 weeks' gestation according to ADIPS criteria (see notes), with an otherwise healthy singleton pregnancy.

Exclusion criteria: women who had special dietary requirements (including vegetarianism/veganism), pre-existing diabetes, or pregnancy achieved by assisted reproduction and those who smoked or consumed alcohol during pregnancy.

Setting: Australia.


InterventionsLow-GI diet group (n = 50): diet GI target of ≤ 50, other nutrients were the same as the comparison group.

High-fibre moderate-GI diet (n = 49): diet GI target of around 60, which represented average GI of Australian population.

All women:

  1. healthy diets of similar protein (15% to 25% total daily energy intake), fat (25% to 30% total daily energy intake), and carbohydrate (40% to 45% total daily energy intake) content;
  2. completed 3-day food record (2 weekdays and 1 weekend day) at baseline and 36-37 weeks' gestation;
  3. received 2 food model booklet to assist in portion size estimation.


OutcomesPregnancy outcomes: birthweight, the need for emergency caesarean section, gestational age at birth, macrosomia, SGA, LGA, ponderal index, neonatal anthropometry (length, head circumference), maternal  metabolic profile in GDM.


Notes
  1. 68% participants in this trial had a BMI < 25 kg/m2.
  2. Insulin treatment was commenced if the mean fasting BGL or 1-h postprandial BGL in the preceding week exceeded 5.2 and 7.5 mmol/L, respectively.
  3. Self-reported pre-pregnancy weight; last weight before delivery was obtained from medical record.
  4. ADIPS criteria used for GDM diagnosis:


  • fasting BGL ≥ 5.5 mmol/L;
  • 2-hour BGL after 75 g glucose load ≥ 8.0 mmol/L;
  • 1 or more value(s) is (are) met or exceeded.


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskDescribed as "the enrolled subjects were centrally randomised to study diet by computer generated random numbers, stratified by BMI and weeks of gestation".

Allocation concealment (selection bias)Low riskDescribed as "the allocation sequence was unpredictable and concealed from the recruiter".

Blinding of participants and personnel (performance bias)
All outcomes
Low riskReported that (besides research dietitian who provided trial intervention) all study personnel and participants were blinded to dietary assignment.

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskReported that the unblinded research dietitian was involved in data collection, no other information on whether or not other outcome assessors were blinded to group allocation.

Incomplete outcome data (attrition bias)
All outcomes
Low riskIn the low-GI group, 1 woman was excluded due to incorrect GDM diagnosis, 3 women withdraw after intervention, 2 women had preterm births, leaving 44 women who completed the study, and 47 women were included in analysis.

In high-fibre group, 2 women withdrew after group allocation, another 2 women withdrew after intervention; 2 women had preterm births, leaving 43 women who completed the study and 45 women who were included in analysis.

Selective reporting (reporting bias)High riskOnly limited data were reported on some of the prespecified review outcomes.

Other biasHigh riskAt baseline, 2-hour post 75 g glucose load BGL for women in low-GI group were significantly higher than those in conventional high-fibre group (mean [SD]: low-GI 8.6 [1.2] mmol/L vs high-fibre group 8.0 [1.3] mmol/L; P = 0.024).

Magee 1990

MethodsRandomised controlled trial.


ParticipantsN = 12.

Obese women (defined as: pre-pregnancy weight > 120% of ideal body weight as specified by the Corrected 1959 Metropolitan Life Insurance table) with GDM according to ADA criteria (see notes).

Exclusion criteria: not reported.

Setting: the United States.


InterventionsDuring the second hospitalised week:

Energy-restricted diet group (n = 7): on an energy-restricted diet of 1200 kcal/day diet by reducing serving size without changing the pattern and content of the diet in the first hospitalised week.

No energy restriction diet group (n = 5): continue the standard diet prescribed as the first week, for about 2400 kcal/day.

All women: hospitalised for the 2 weeks duration. Studies and diet during the first week were identical for all patients.

During the first hospitalised week:

  1. dietary pattern: 25% total energy for breakfast, lunch and dinner. 12.5% total energy for afternoon tea and supper;
  2. diet contents were: 50% carbohydrate, 30% fat, 20% protein, with 11 g of total dietary fibre per 500kcal;
  3. daily morning double-voided urine sample for ketone and fasting plasma glucose;
  4. on the sixth day of each week: blood after overnight fast for plasma glucose, insulin, triglyceride, free fatty acids, glycerol, β-hydroxhbutyrate. A glucose profile with 25 samples drawn over 24 hrs was initiated as well on the same day;
  5. on the seventh day of each week: repeat fasting blood work as day 6 and a 3-h 100-g OGTT.


OutcomesMetabolic profile including plasma glucose, fasting plasma insulin, urine ketones.


NotesADA criteria used for GDM diagnosis:

  • 2 or more values meeting the following in 100g 3-h OGTT;
  • fasting 5.3 mmol/L;
  • 1-h: 10 mmol/L;
  • 2-h: 8.6 mmol/L;
  • 3-h: 7.8 mmol/L.


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskDescribed as ”subjects were randomised to the control or calorie-restricted group”.

Allocation concealment (selection bias)Unclear riskNo information was given on allocation concealment.

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskNo information on whether participants or research personnel were blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNo information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes
Low riskNo loss to follow-up or post randomisation exclusions reported.

Selective reporting (reporting bias)High riskNone of the clinical outcomes prespecified in this review was reported.

Other biasLow riskThere is no obvious risk of other bias.

Moses 2009

MethodsRandomised controlled trial.


ParticipantsN = 63.

Women aged at 18 to 40 years (inclusive) diagnosed with GDM according to ADIPS criteria (see notes), singleton pregnancy, no previous GDM, non-smoker, and seen for the first dietary visit between 28 and 32 weeks of gestation, and ability to follow the protocol requirements.

Exclusion criteria: any condition or medication that could affect glucose levels and unwillingness to follow the prescribed diet.

Setting: Australia.


InterventionsLow-GI diet group (n = 31):

diet based on previously verified low–glycaemic index food, including pasta, grain breads, and unprocessed breakfast cereals with a high-fibre content. Women were specifically asked to avoid consuming white bread, processed commercial breakfast cereals, potatoes, and some rice varieties.

Conventional high-fibre, low-sugar, higher-GI diet group (n = 32):

women were advised to follow a diet with a high-fibre and low-sugar content, with no specific mention of the GI. Potatoes, whole wheat bread, and specific high-fibre, moderate-to-high GI breakfast cereals were recommended.

All women:

  1. were provided with a home glucose meter and were asked to test after fasting and 1 hour after the start of each of their 3 major meals at least every second day;
  2. had at least 4 times diabetes centre visit with dietitian for dietary assessment and if they required insulin were seen as many times as necessary for insulin adjustment;
  3. were provided with a booklet outlining the carbohydrate choices the carbohydrate food amounts constituting 1 serving (based on 15 g portions);
  4. were advised to consume 3 small meals and 2 to 3 snacks with a specified number of servings of carbohydrate.


OutcomesMethod of delivery, macrosomia, LGA, induction of labour, preterm birth, birthweight, infant anthropometric outcomes, Apgar score.


NotesADIPS criteria used for GDM diagnosis:

  • fasting BGL ≥ 5.5 mmol/L;
  • 2-hour BGL after 75 g glucose load ≥ 8.0 mmol/L;
  • 1 or more value(s) is (are) met or exceeded.


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskDescribed as: “participants were randomly assigned to receive one of two different diets using permuted blocks of unequal size with the list generated using STATA (Version 7.0)”.

Allocation concealment (selection bias)Low riskMethod of generation of randomisation sequence likely to have concealed allocation.

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskParticipants and study dietitian were not blinded. The physician caring for the patients was blinded to group allocation.

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNo information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes
Low riskNo loss to follow-up or post randomisation exclusion.

Selective reporting (reporting bias)High riskMost of the prespecified review outcomes were not reported in this trial.

Other biasLow riskThere is no obvious risk of other bias.

Rae 2000

MethodsRandomised controlled trial.


ParticipantsN = 125; N = 117 women involved in analysis (8 withdraw).

Women at ≤ 35 weeks 6 days gestation; > 110% of ideal body weight for height (adjusted for expected pregnancy weight gain and using a BMI of 25 as equal to 100% ideal body weight); fasting BGL > 5.4 mmol/L and or 2 hour BGL > 7.9 mmol/L in 75 g 2 hour OGTT.

Exclusion criteria: not reported.

Setting: Australia.


InterventionsEnergy-restricted diet group (30% energy restriction) (n = 67 with outcome data available for 63 women): women on a diabetic diet providing between 6800 and 7600 kJ energy per day, which represented 70% of the Recommended Dietary Intake for pregnancy women (National Health and Medical Research Council of Australia).

No energy restriction diet group (n = 58 with outcome data available for 54 women): women on diabetic diet without energy restriction, providing 8600 to 9500 kJ energy per day.

All women:

  1. diabetes education provided by a research dietitian at each antenatal visit;
  2. hyperglycaemia control, BGL self-monitoring: before and 2 hours after each meal (6 times per day), for a minimum of 2 days each week;
  3. fetal and maternal surveillance and anticipated term delivery;
  4. use of insulin decided by medical staffs that were blinded to group allocation. Criteria for insulin: fasting BGL > 5.5 mmol/L or 2-h BGL > 7.0 mmol/L on two or more occasions in any 72 hours period at the same pre- or post-prandial epoch;
  5. metabolic monitoring for HbA1c, serum beta-hydroxybutyrate, urinary ketone;
  6. 3-day food intake dairies for adherence to diet.


OutcomesMacrosomia, newborns anthropometric measurement at 5 days of age, maternal dietary intake.


Notes
  • Women's BMI at GDM diagnosis mean [SD] was 37.9 [0.7] and 38.9 [0.7] for women in intervention group and control group, respectively.
  • Due to the adherence to the dietary intervention, there was no significant difference in total energy intake between groups.
  • 7 sets of twins were included in the study, 3 sets in the intervention group and 4 sets in the control group.


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskDescribed as “women were allocated at random by draw of opaque numbered envelopes”.

Allocation concealment (selection bias)Unclear riskDescribed as above. It is likely adequately done.

Blinding of participants and personnel (performance bias)
All outcomes
Low riskParticipants and diabetes service staff were blinded to allocation to diet group.

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskDescribed as that "demographic, obstetric and neonatal data were collected prospectively'. No information on whether or not outcome assessors were blinded to group allocation.

Incomplete outcome data (attrition bias)
All outcomes
Low riskA total of 8 women (6.4%) (four from each group) withdrew and were excluded from data analysis; reasons for withdraw and baseline details about these eight women were not given.

Some data points have small numbers of lost participants that are unexplained in the text, although this is unlikely to have affected the overall results. 

Selective reporting (reporting bias)High riskMost of the prespecified review outcomes were not reported in this trial.

Outcomes including shoulder dystocia, birthweight, gestational age at birth were reported in one trial. However, as it was unclear about the sample sizes in each study groups for each of these reported outcomes, hence, no data were able to be included in the review.

Other biasLow riskThere is no obvious risk of other bias.

Reece 1995

MethodsRandomised controlled trial.


ParticipantsN = 22.

Women diagnosed with GDM between 24-29 weeks' gestation.

Exclusion criteria: diagnosis of GDM after 29 weeks' gestation.

Setting: United States.


InterventionsADA diet group (n = 11): diet containing 20 g fibre per day; 30% daily energy intake derived from fat, and 50% derived from carbohydrate.

Fibre-enriched diet group (n = 11): diet containing 80 g fibre per day; 20% daily energy intake derived from fat, and 60% derived from carbohydrate.

All women:

capillary BGL 6 times a day (before and after each meal), twice weekly.


OutcomesGestational weight gain, insulin required for hyperglycaemia, birthweight, gestational age at birth.


NotesGDM diagnostic criteria not reported.


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Low riskRandomisation was done by using a random numbers table.

Allocation concealment (selection bias)Unclear riskNot reported.

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskParticipants were unlikely to be blinded.

The research dietitian and the diabetes nurse specialist who were responsible for monitoring diet compliance and glycaemic control were unlikely to be blinded.

Unclear about whether other research personnel were blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes
Unclear riskNo information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes
Unclear riskWomen with insulin-dependent diabetes and GDM were included in the trial. It was reported that 11/61 women (5 in the ADA diet group and 6 in the fibre-enriched diet) were excluded from the study after randomisation: one had a spontaneous abortion, 2 moved away, and 4 from each group were noncompliant.

It is unclear how many of these 11 women excluded after randomisation were women with GDM.

Selective reporting (reporting bias)High riskMost of the prespecified review outcomes were not reported in this trial.

Other biasLow riskThere is no obvious risk of other bias.

 
Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion

Gillen 2004Study compared standard clinical care only for women with GDM with standard clinical care with additional advice targeting intakes of foods rich in unsaturated fats.

Gillmer 1986Study compared diet alone with diet and insulin for GDM management, did not meet the inclusion criteria of this review for interventions.

Ilic 1999Women in one group had a meal containing saturated fat and women in the other group had a meal containing monounsaturated fat. 2 weeks later, women in the 2 groups swapped to have the other group's meal.

Not meeting the inclusion criteria for eligible interventions for this review.

Knopp 1991A literature review on management of GDM.

Ma 2011Participants were also instructed to increase exercise level by adding daily walking activity.

Nolan 1984A randomised cross-over study.

Reader 2006Trial did not compare different types of dietary advice, but compared different types of care for women with GDM. Women in the intervention group were cared according to the nutrition practice guidelines for GDM, that emphasised 3 major areas of setting individualised medical nutrition therapy goals, BGL monitoring, a minimum of 3 nutrition visits with follow ups via phone or in person. Women in the control group received usual prenatal nutrition care.

 
Comparison 1. Low-moderate GI food versus high-moderate food

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Macrosomia (birthweight greater than 4000 g)289Risk Ratio (M-H, Fixed, 95% CI)0.45 [0.10, 2.08]

 2 Large-for-gestational age (birthweight ≥ 90th percentile for gestational age)289Risk Ratio (M-H, Fixed, 95% CI)0.95 [0.27, 3.36]

 3 Caesarean section163Risk Ratio (M-H, Fixed, 95% CI)0.66 [0.29, 1.47]

 4 Operative vaginal birth163Risk Ratio (M-H, Fixed, 95% CI)0.62 [0.16, 2.37]

 5 Normal vaginal birth163Risk Ratio (M-H, Fixed, 95% CI)1.35 [0.89, 2.07]

 6 Birthweight (g)162Mean Difference (IV, Fixed, 95% CI)-50.70 [-272.56, 171.16]

 7 Gestational age at birth162Mean Difference (IV, Fixed, 95% CI)0.30 [-0.30, 0.90]

 8 Small-for-gestational age163Risk Ratio (M-H, Fixed, 95% CI)5.16 [0.26, 103.27]

 9 Induction of labour163Risk Ratio (M-H, Fixed, 95% CI)0.88 [0.33, 2.34]

 10 Preterm birth (< 37 weeks' gestation)163Risk Ratio (M-H, Fixed, 95% CI)0.52 [0.05, 5.41]

 11 Insulin or oral hypoglycaemic agent required for hyperglycaemia3126Risk Ratio (M-H, Random, 95% CI)0.85 [0.37, 1.93]

 
Comparison 2. Low-GI diet versus high-fibre moderate-GI diet

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Macrosomia (birthweight greater than 4000 g)192Risk Ratio (M-H, Fixed, 95% CI)0.32 [0.03, 2.96]

 2 Large-for-gestational age (birthweight ≥ 90th percentile for gestational age)192Risk Ratio (M-H, Fixed, 95% CI)2.87 [0.61, 13.50]

 3 Caesarean section188Risk Ratio (M-H, Fixed, 95% CI)1.8 [0.66, 4.94]

 4 Birthweight (g)192Mean Difference (IV, Fixed, 95% CI)0.0 [-277.18, 277.18]

 5 Gestational age at birth (weeks)192Mean Difference (IV, Fixed, 95% CI)-0.10 [-0.39, 0.19]

 6 Preterm birth192Risk Ratio (M-H, Fixed, 95% CI)0.96 [0.14, 6.51]

 7 Small-for-gestational age192Risk Ratio (M-H, Fixed, 95% CI)1.20 [0.34, 4.18]

 8 Ponderal index (kg/m3)192Mean Difference (IV, Fixed, 95% CI)0.20 [-0.79, 1.19]

 9 Weight gain during pregnancy (kg)187Mean Difference (IV, Fixed, 95% CI)-1.20 [-3.43, 1.03]

 10 Adherence to dietary intervention192Risk Ratio (M-H, Fixed, 95% CI)0.84 [0.64, 1.11]

 11 Insulin required for hyperglycaemia192Risk Ratio (M-H, Fixed, 95% CI)0.83 [0.58, 1.17]

 
Comparison 3. Energy-restricted diet versus no energy restriction diet

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Fetal mortality1124Risk Ratio (M-H, Fixed, 95% CI)0.0 [0.0, 0.0]

 2 Macrosomia1122Risk Ratio (M-H, Fixed, 95% CI)1.56 [0.61, 3.94]

 3 Large-for-gestational age1123Risk Ratio (M-H, Fixed, 95% CI)1.17 [0.65, 2.12]

 4 Caesarean section1121Risk Ratio (M-H, Fixed, 95% CI)1.18 [0.74, 1.89]

 5 Operative vaginal birth1121Risk Ratio (M-H, Fixed, 95% CI)0.98 [0.38, 2.54]

 6 Normal vaginal birth1121Risk Ratio (M-H, Fixed, 95% CI)0.89 [0.63, 1.27]

 7 Induction of labour1114Risk Ratio (M-H, Fixed, 95% CI)1.02 [0.68, 1.53]

 8 Pre-eclampsia1117Risk Ratio (M-H, Fixed, 95% CI)1.0 [0.51, 1.97]

 9 Insulin or oral hypoglycaemic agent required for hyperglycaemia1117Risk Ratio (M-H, Fixed, 95% CI)1.05 [0.47, 2.34]

 10 Insulin sensitivity1Std. Mean Difference (IV, Fixed, 95% CI)Subtotals only

    10.1 Fasting plasma glucose (mmol)
112Std. Mean Difference (IV, Fixed, 95% CI)-0.35 [-1.51, 0.81]

    10.2 Fasting plasma insulin (pM)
112Std. Mean Difference (IV, Fixed, 95% CI)-0.17 [-1.32, 0.98]

 
Comparison 4. Low-carbohydrate (CHO) diet (≤ 45% total energy from CHO) versus high-CHO diet (≥ 50% total energy from CHO)

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Macrosomia (birthweight greater than 4000 g)130Risk Ratio (M-H, Fixed, 95% CI)0.0 [0.0, 0.0]

 2 Caesarean section130Risk Ratio (M-H, Fixed, 95% CI)1.4 [0.57, 3.43]

 3 Operative vaginal birth130Risk Ratio (M-H, Fixed, 95% CI)1.0 [0.07, 14.55]

 4 Normal vaginal birth130Risk Ratio (M-H, Fixed, 95% CI)0.78 [0.39, 1.54]

 5 Birthweight (g)130Mean Difference (IV, Fixed, 95% CI)22.0 [-241.06, 285.06]

 6 Gestational age at birth (weeks)130Mean Difference (IV, Fixed, 95% CI)0.10 [-0.83, 1.03]

 
Comparison 5. High-monounsaturated fat (MUFA) diet (≥ 20% total energy from MUFA) versus high-CHO diet (≥ 50% total energy from CHO)

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Macrosomia (birthweight greater than 4000 g)127Risk Ratio (M-H, Fixed, 95% CI)0.65 [0.19, 2.18]

 2 Large-for-gestational age127Risk Ratio (M-H, Fixed, 95% CI)0.54 [0.21, 1.37]

 3 Birthweight (g)127Mean Difference (IV, Fixed, 95% CI)1.0 [-112.85, 114.85]

 4 Gestational age at birth (weeks)127Mean Difference (IV, Fixed, 95% CI)0.10 [-0.13, 0.33]

 5 Pre-eclampsia127Risk Ratio (M-H, Fixed, 95% CI)0.0 [0.0, 0.0]

 6 Insulin or oral hypoglycaemic agent required for hyperglycaemia127Risk Ratio (M-H, Fixed, 95% CI)0.0 [0.0, 0.0]

 7 Maternal weight at late pregnancy (third trimester) (kg)1Mean Difference (IV, Fixed, 95% CI)Subtotals only

    7.1 Maternal weight at 36 weeks' gestation
127Mean Difference (IV, Fixed, 95% CI)12.60 [7.93, 17.27]

    7.2 Maternal weight at 38 weeks' gestation
127Mean Difference (IV, Fixed, 95% CI)11.80 [7.23, 16.37]

    7.3 Maternal weight at delivery
127Mean Difference (IV, Fixed, 95% CI)11.90 [7.47, 16.33]

 8 Maternal BMI at late pregnancy (third trimester) (kg/m2)1Mean Difference (IV, Fixed, 95% CI)Subtotals only

    8.1 Maternal BMI at 36 weeks' gestation (kg/m2)
127Mean Difference (IV, Fixed, 95% CI)4.70 [3.18, 6.22]

    8.2 Maternal BMI at 38 weeks' gestation (kg/m2)
127Mean Difference (IV, Fixed, 95% CI)3.80 [2.22, 5.38]

    8.3 Maternal BMI at delivery (kg/m2)
127Mean Difference (IV, Fixed, 95% CI)3.90 [2.41, 5.39]

 9 Maternal postpartum BMI (> 4 months postpartum) (kg/m2)127Mean Difference (IV, Fixed, 95% CI)4.10 [2.34, 5.86]

 10 Development of type 2 diabetes1Risk Ratio (M-H, Fixed, 95% CI)Subtotals only

    10.1 Diagnosed by OGTT at early postnatal period (within 6 weeks postpartum)
124Risk Ratio (M-H, Fixed, 95% CI)2.0 [0.45, 8.94]

    10.2 Diagnosed by OGTT at ≥ 4 months postpartum
16Risk Ratio (M-H, Fixed, 95% CI)1.0 [0.10, 9.61]

 11 Development of glucose intolerance without meeting type 2 diabetes diagnostic criteria1Risk Ratio (M-H, Fixed, 95% CI)Subtotals only

    11.1 Diagnosed by OGTT at early postnatal period (within 6 weeks postpartum)
124Risk Ratio (M-H, Fixed, 95% CI)1.5 [0.30, 7.43]

    11.2 Diagnosed by OGTT at ≥ 4 months postpartum
17Risk Ratio (M-H, Fixed, 95% CI)0.27 [0.01, 4.93]

 
Comparison 6. Standard ADA diet (20 g fibre/day) versus fibre-enriched diet (80 g fibre/ day)

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Birthweight (g)122Mean Difference (IV, Fixed, 95% CI)-94.0 [-446.71, 258.71]

 2 Gestational age at birth (weeks)122Mean Difference (IV, Fixed, 95% CI)0.0 [-1.30, 1.30]

 3 Insulin or oral hypoglycaemic agent required for hyperglycaemia122Risk Ratio (M-H, Fixed, 95% CI)0.0 [0.0, 0.0]

 4 Gestational weight gain (kg)122Mean Difference (IV, Fixed, 95% CI)2.40 [-2.20, 7.00]