Dietary guideline adherence during preconception and pregnancy: A systematic review.

Abstract The aim of this study is to determine the level of adherence to dietary guidelines among men and women during preconception, and pregnant women, and factors associated with adherence. Searches were conducted in CINAHL, AMED, EMBASE, and Maternity and Infant Care from inception to March 2018. Observational studies assessing the primary outcome (adherence to dietary guidelines and/or nutritional recommendations) and/or secondary outcome (factors associated with adherence) were eligible. Study quality was assessed using the National Institutes of Health Quality Assessment Tool for Observational Cohort and Cross‐sectional studies. Men or women (aged ≥18 years) who identified as trying/intending to conceive or were pregnant. Eighteen studies were included. The quality of studies was fair (44%) to good (56%). Most studies indicated preconceptual and pregnant women do not meet recommendations for vegetable, cereal grain, or folate intake. Pregnant women did not meet iron or calcium intake requirements in 91% and 55% of included studies, respectively, and also exceeded fat intake recommendations in 55% of included studies. Higher level education was associated with improved guideline adherence in pregnant women, whereas older age and non‐smoking status were associated with greater guideline adherence in preconceptual and pregnant women. The findings of this review suggest that preconceptual and pregnant women may not be meeting the minimum requirements stipulated in dietary guidelines and/or nutritional recommendations. This could have potential adverse consequences for pregnancy and birth outcomes and the health of the offspring. Major knowledge gaps identified in this review, which warrant further investigation, are the dietary intakes of men during preconception, and the predictors of guideline adherence.

Multiple factors can impact guideline adherence, including income, food availability and affordability, individual beliefs and preferences, cultural traditions, and educational, social, geographical, and environmental aspects (WHO, 2015). This sociocultural context can exert considerable influence on a diet at different stages of life; in particular, during conception and pregnancy (Withers, Kharazmi, & Lim, 2018).
Poor adherence to dietary guidelines or nutritional recommendations during the preconception period (i.e., the weeks to months before pregnancy occurs) and throughout pregnancy can have a negative impact on fertility, pregnancy and birth outcomes, as well as the future health of the offspring (Craig, Jenkins, Carrell, & Hotaling, 2017;Lane, Robker, & Robertson, 2014;Stephenson et al., 2018). For example, in women, adequate intake of folate during the preconception period may help to prevent neural tube defects in the foetus (De-Regil, Peña-Rosas, Fernández-Gaxiola, & Rayco-Solon, 2015;WHO, 2017).
Parental dietary factors are also implicated in the development of disease in the offspring (Fleming et al., 2018). Preventable noncommunicable diseases in the offspring, including cardiovascular diseases, diabetes, cancer, chronic respiratory diseases, atopic disease, and neurological disorders, have been attributed to parental health (physiology, metabolic factors, and body composition) and nutrition status at the time of conception (Fleming et al., 2018). During pregnancy, a healthy diet may prevent excessive weight gain and the associated risks of gestational diabetes, hypertension, or preeclampsia (Schoenaker, Soedamah-Muthu, Callaway, & Mishra, 2015;Stephenson et al., 2018). A healthy diet also may assist in the prevention of low birth weight infants, macrosomia, preterm birth, stillbirth, and maternal anaemia (World Health Organisation, 2016).
Although non-adherence to national dietary guidelines and nutritional recommendations is a global issue (WHO, 2015), it is not clear to what extent non-adherence applies to individuals in the preconception period and during pregnancy. Understanding the level of concordance with dietary guidelines in these populations, as well as the factors impacting adherence, may help to inform the development of future policies and/or practices specifically targeted at improving dietary practices during the preconception period and throughout pregnancy.

| METHODS
This systematic literature review was conducted and reported in accordance with the preferred reporting items for systematic reviews and meta-analysis: the PRISMA statement (Moher, Liberati, Tetzlaff, & Altman, 2009).

Key messages
• Dietary guidelines exist to promote health and well-being through the prevention of diet-related disorders and nutritional deficiencies.
• Non-adherence during the preconception period and pregnancy may have a negative impact on fertility, pregnancy and birth outcomes, and the health of the offspring.
• Sociodemographic factors are associated with compliance to dietary guidelines.
• Understanding the factors associated with adherence and non-adherence can inform future policy and practice aimed at improving overall dietary guideline compliance, during the preconception period and pregnancy.
• Nutrition education and counselling may improve compliance; however, further studies are needed to determine how the intervention translates to maternal and infant health outcomes.

| Objectives
The aim of this systematic review was to determine the level of adherence to national/international dietary guidelines in their entirety, among adult men and women during the preconception period, and in pregnant women, and the factors associated with adherence.

| Search strategy
Literature searches were conducted in five electronic databases from their inception to March 22, 2018.

| Types of exposures
Studies observing the usual dietary and/or nutritional intake, and/or dietary habits of participants, the components of which were derived from foodstuffs and beverages, were eligible for inclusion. Studies assessing nutrient intakes arrived from supplement use were excluded, as were studies examining isolated or limited numbers of nutrients (i.e., omega-3 fatty acids, iodine, calcium, or iron) or limited components of the diet (i.e., total energy or fibre), as these studies cannot be compared with dietary guidelines to determine overall adherence.
Also excluded were studies involving participants receiving parenteral nutrition, feeds via percutaneous gastrostomy tubes, and those with special dietary needs (i.e., due to allergy).

| Types of outcome measures
The primary outcome was the level of adherence to national/ international dietary guidelines and/or recommendations in full; this could be reported using any measure of adherence. The secondary outcome was the factors associated with the level of guideline adherence; this was not limited to any type of factor or association.

| Study selection
The title and abstract of all articles were screened by the lead reviewer (CC) against the predefined inclusion and exclusion criteria ( Figure 1).
Potentially eligible articles were retrieved as full-text and screened by CC. Two second reviewers (ML or AS), with methodological and content expertise, used the liberal accelerated approach (Khangura, Konnyu, Cushman, Grimshaw, & Moher, 2012) to randomly review 10% of included studies and 10% of excluded studies. Any disagreements were discussed until consensus was reached. If unresolved, another reviewer (ML or AS) was invited to adjudicate ( Figure 1). OR "food habits" OR "food survey" OR "food intake" OR "food frequency" OR "dietary practices" OR nutrition OR "nutritional intake" OR "nutrition survey" 578,150 5 Dietary guidelines [MeSH] OR "food policy" OR "nutrition guidelines" OR "nutrition policy" OR "dietary recommendations" OR "dietary reference intake" OR "eating guidelines" OR "daily recommended allowance" OR "daily recommended intake" OR "reference daily intake."

| Data synthesis
Given the descriptive nature of this review, the analysis of included studies was undertaken in a narrative manner.

| RESULTS
Database searches retrieved 722 articles, and an additional five articles were found by manually searching the reference lists of included studies. After the removal of duplicates, 565 articles remained. Of these, 524 were removed at the title/abstract screening stage, and          (Continues) 23 removed at the full-text screening stage as they did not meet the eligibility criteria (Figure 1). A total of 18 studies met the inclusion criteria for this review.
The authors of these studies were contacted for further information; however, no response was received from any author.

| Dietary intake in the preconception period
Of the two studies reporting dietary intake as food groups, evidence indicated that most women in the preconception period did not achieve the recommended daily intake of vegetables (Bojar et al., 2006;Okubo et al., 2011) and cereals (Bojar et al., 2006;Okubo et al., 2011), but most frequently met requirements for dairy intake (Bojar et al., 2006). Of the three studies reporting dietary intake as nutrients, the consumption of folate (Hure et al., 2009;Pinto et al., 2009) and vitamin E (Hure et al., 2009;Pinto et al., 2009) was most frequently reported as being inadequate in the diets of preconceptual women. On the other hand, protein intake was more likely to exceed daily recommendations (de Weerd et al., 2003;Olmedo-Requena et al., 2017).

| Factors predicting adherence
Nine studies reported on factors predicting guideline adherence in pregnancy. Most of these studies reported a statistically significant association between higher level of education (Bojar et al., 2006;Okubo et al., 2011;Panwar & Punia, 1998;Yang et al., 2017), older age (Bojar et al., 2006;Okubo et al., 2011;Olmedo-Requena et al., 2017), or non-smoking status (Malek et al., 2016;Okubo et al., 2011;Olmedo-Requena et al., 2017) and adherence to dietary guidelines or nutritional recommendations. The impact of residential location on guideline adherence was contradictory; two studies (Bojar et al., 2006;Malek et al., 2016) reported a statistically significant positive association between level of guideline adherence and living in non-metropolitan residences, whereas two studies (Gao et al., 2013;Yang et al., 2017) found a statistically significant positive association between level of adherence and living in urban residences. Only one study (Olmedo-Requena et al., 2017) reported on factors associated with guideline adherence among women during the preconception period. This study found a statistically significant association between guideline adherence and higher social class, non-smoking status, increased physical activity, and older age.  Our findings also indicate that fat intake among pregnant women may exceed recommended levels stipulated in national/international dietary guidelines. However, it is important to note that the included studies assessing fat consumption only reported total fat intake (Liu et al., 2015;Panwar & Punia, 1998;Yang et al., 2017) or the combination of fats and oils (Dahiya, 2002;Gao et al., 2013;Jood et al., 2002).
In other words, these studies did not differentiate between the types of fats consumed in the diet, such as saturated fats, trans fats, and omega-3/omega-9 fatty acids. In light of emerging clinical evidence linking omega-3 fatty acid intake in pregnancy to improvements in infant cognitive development (Braarud et al., 2018), and the prevention of allergic disease (Best, Gold, Kennedy, Martin, & Makrides, 2016), this information would have been beneficial. Notwithstanding, the finding that total dietary fat intake exceeded recommendations (i.e., 30% of total energy) is still clinically significant given that this may potentially contribute to unhealthy maternal weight gain (World Health Organisation, 2015). The impact of this weight gain for both the mother and infant can be considerable, with maternal obesity shown in multiple systematic reviews (Marchi, Berg, Dencker, Olander, & Begley, 2015) to be associated with an increased risk of preeclampsia, gestational diabetes, macrosomia, congenital abnormalities, still birth, low birthweight infants, and maternal mortality (Marchi et al., 2015).  & Hagag, 2018). Strategies aimed at improving nutrition and health behaviours before conception also have been explored. One framework recently described by Barker et al. (2018) acknowledges the importance of identifying the age and life phase of an individual; this may help to identify the individual's motivations and likely receptiveness to different intervention types, thus enabling a clinician to deliver a more targeted approach to preconception management (Barker et al., 2018). Additionally, Barker et al. (2018) suggest that an intervention framework should combine public health policy with strategic engagement from the private sector in order to further improve health outcomes (Barker et al., 2018). Of course, further work is needed to determine whether such an approach actually translates into improvements in maternal and infant outcomes.
An important knowledge gap identified through this review is the absence of any studies examining dietary intake in males during the preconception period (i.e., the male partner of a woman trying to conceive), and despite having an important role to play in preconception, men have been largely overlooked in the literature to date (Kotelchuck & Lu, 2017). This represents a much needed area for future research, for several reasons. First, epigenetic changes to the DNA of spermatozoa may be accelerated through nutrition and lifestyle factors, and these changes may have long-lasting transgenerational effects (Lane et al., 2014). Second, paternal obesity has implications for fertility, in particular, an association with disturbed endocrinology, erectile dysfunction, and increased sperm DNA fragmentation (El Salam, 2018). Indeed, reduced rates of clinical pregnancies in assisted reproductive cycles utilizing sperm of obese men have been observed (Mushtaq et al., 2018). Evidence also suggests that the offspring of obese fathers may result in metabolic changes within the offspring and the subsequent inheritance of obesity (Craig et al., 2017). A better understanding of the nutritional status of males during the preconception period, as well as the factors impacting nutrition in this population, would help to provide a targeted approach for couples experiencing infertility.
Several limitations exist within this review. One limitation is the heterogeneity of instruments used to assess dietary intake. Some studies used dietary recall methods and others FFQs; there was also great variability in reported time frames, ranging from 24 hr to 12 months. These differences in outcomes and outcome measures, and the disparities in how data were reported, meant the pooling of data for meta-analysis was not possible. Lastly, the dietary intakes reported in the included studies were assessed for adherence against 13 various national food-based dietary guidelines (i.e., food groups) and/or national or international nutritional recommendations (i.e., RNI/RDA/ EAR/AI/UL), dependent upon the country the study was conducted.
Given that the recommendations reported in each of these guidelines may differ to some extent, it is possible that adherence (or nonadherence) to one guideline may not be necessarily transferable to all dietary guidelines. Although beyond the scope of this review, comparisons between countries/regions that utilize RNI/RDA/EAR/AI/UL for nutritional recommendations and food-based dietary guidelines would be an interesting area for future research to determine how well the two approaches align. For example, a sensitivity and specificity analysis could explore whether populations meeting food group serving recommendations also meet RNI/RDA/EAR/AI/UL recommendations.

| CONCLUSION
The consumption of a healthy diet during the preconception period and pregnancy can be achieved by adhering to national/international dietary guidelines and/or nutritional recommendations. Concordance with these guidelines should provide some assurance that energy, macronutrient, and micronutrient intake are adequate to support fertility, pregnancy, and positive birth outcomes, as well as the future health of the offspring. The findings from this review indicate that women both in the preconception period and throughout pregnancy may be falling short of targets stipulated in dietary guidelines and nutrient recommendations. In particular, preconceptual and pregnant women may not be consuming enough vegetables, cereal grains, folate, iron, and calcium and may be consuming excess fat. A number of demographic factors were shown to impact guideline adherence, which could have implications for both future policy and practice.
However, further research is needed to assess the predictors of guideline adherence for both men and women in the preconception period, as well as the quality of diets of men during preconception.

ACKNOWLEDGMENTS
We would like to thank the reviewers for their generous time and helpful feedback on our manuscript throughout the peer-review process.

CONFLICT OF INTEREST
The authors declare that they have no conflicts of interest.

FINANCIAL SUPPORT
None.

CONTRIBUTIONS
CC formulated the research question and undertook the database searches, study selection, data extraction, and critical appraisal. AS and ML contributed to the design of the research question, served as second reviewers at the study selection, data extraction, and critical appraisal phases and contributed to manuscript drafting. All authors approved the final manuscript before submission.