ABSTRACT
Background
This systematic review was conducted by the 2025 Dietary Guidelines Advisory Committee as part of the process to develop the Dietary Guidelines for Americans, 2025-2030. The U.S. Departments of Health and Human Services (HHS) and Agriculture (USDA) appointed the 2025 Dietary Guidelines Advisory Committee (Committee) in January 2023 to review evidence on high priority scientific questions related to diet and health. Their review forms the basis of their independent, science-based advice and recommendations to HHS and USDA, which is considered as the Departments develop the next edition of the Dietary Guidelines. As part of that process, the Committee conducted a systematic review with support from the USDA Nutrition Evidence Systematic Review (NESR) team to answer the following question: What is the relationship between dietary patterns consumed during pregnancy and birth weight? This review is an update to an existing review that was conducted by the Pregnancy Technical Expert Collaborative of the Pregnancy and Birth to 24 Months Project.
Methods
The Committee conducted a systematic review using the methodology of the USDA NESR team. The Committee first developed a protocol. The intervention/exposure was dietary patterns consumed during pregnancy, the comparators are different dietary patterns or different levels of adherence to/consumption of the same dietary pattern, and the outcomes were intrauterine growth restriction, small-for-gestational age, large-for gestational age, low birth weight, and macrosomia. Additional inclusion criteria were established for the following study characteristics: a) use randomized or non-randomized controlled trial, prospective or retrospective cohort, or nested case-control study designs, b) be published in English in peer-reviewed journals, c) be from countries classified as high or very high on the Human Development Index, and d) enroll participants with a range of health statuses. The review excluded studies that exclusively enrolled participants with a disease or that did not control for at least 1 of the key confounders listed in the analytic framework.
NESR librarians conducted a literature search in PubMed, Embase, CINAHL, and Cochrane to identify articles published between January 2017 and January 2024. Two NESR analysts independently screened all electronic results and the reference lists of included articles based on the pre-determined criteria. The results of this search were combined with included articles from the existing review.
NESR analysts extracted data, from each included article, with a second analyst verifying accuracy of the extraction. Two NESR analysts independently conducted a formal risk of bias assessment, by study design, for each included article, then reconciled any differences in the assessment. The Committee qualitatively synthesized the evidence, from all included articles identified in the updated literature search and from the existing review, according to the synthesis plan, with attention given to the overarching themes or key concepts from the findings, similarities and differences between studies, and factors that may have affected the results. The Committee developed conclusion statements and graded the strength of evidence based on its consistency, precision, risk of bias, directness, and generalizability.
Results
Small-for-gestational age
Conclusion statement and grade:
Dietary patterns consumed during pregnancy that are characterized by higher intakes of vegetables, fruits, legumes, nuts and seeds, grains, fish/seafood, dairy, and unsaturated fats, and lower intakes of red and processed meat, added sugars, and saturated fats may be associated with lower risk of small-for-gestational age in infants. This conclusion statement is based on evidence graded as limited.
(Grade: Limited)
Summary of the evidence:
• Forty-nine articles examined dietary patterns consumed during pregnancy and small-for-gestational age. Forty-two articles were from prospective cohort studies, 8 articles were from randomized controlled trials, and 1 article was also a non-randomized controlled trial.
• The direction and size of effects differed across studies.
• The size of groups was too small in some studies. Variation around the effect estimates were wide in some studies.
• Few studies were designed and conducted well.
• The interventions/exposures and outcomes that were examined do not directly represent those of interest in this review.
• The evidence may not apply to the U.S. population.
Large-for-gestational age, low birth weight, and macrosomia
Conclusion statement and grade:
A conclusion statement cannot be drawn about the relationship between dietary patterns consumed during pregnancy and risk of large-for-gestational age, low birth weight, and macrosomia in infants because of substantial concerns with consistency, risk of bias, and generalizability in the body of evidence. (Grade: Grade Not Assignable)
Summary of the evidence:
• Forty-five articles examined dietary patterns consumed during pregnancy and large-for-gestational age, low birth weight, and/or macrosomia. Thirty-six articles were from prospective cohort studies, 8 articles were from randomized controlled trials, and 1 article was also a non-randomized controlled trial.
• The direction and size of effects and the dietary patterns varied widely.
• Few studies were designed and conducted well.
• Generalizability of the body of evidence to the U.S. population, both in terms of participant characteristics and the dietary patterns, was limited.