What is the question?

• The question is: What is the relationship between dietary patterns consumed during pregnancy and gestational age at birth? The populations or life-stages of interest for this question is pregnancy and infants at birth.

Why was this question asked?

• 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.

How was this question answered?

• The Committee conducted a systematic review to answer this question with support from the USDA Nutrition Evidence Systematic Review team. This review updated an existing review that was conducted as part of the Pregnancy and Birth to 24 Months Project.

What is the answer to the question?

• Dietary patterns consumed during pregnancy may not be associated with risk of preterm birth. This conclusion statement is based on evidence graded as limited.

How up-to-date is this systematic review?

• The conclusion statement from this review is based on articles published between January 1980 and January 2024.

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 gestational age at birth? This review is an update to an existing review that was conducted as part 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 were different dietary patterns or different levels of adherence to/consumption of the same dietary pattern, and the outcome was preterm birth. 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 one 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 a conclusion statement and graded the strength of evidence based on its consistency, precision, risk of bias, directness, and generalizability.

Results

Dietary patterns and gestational age at birth

Conclusion statement and grade

• Dietary patterns consumed during pregnancy may not be associated with risk of preterm birth. This conclusion statement is based on evidence graded as limited. (Grade: Limited)

Summary of the evidence

• Forty articles met the inclusion criteria for this review. Thirty articles were from prospective cohort studies, 10 articles were from randomized controlled trials, and one 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 many studies. Variation around the effect estimates were wide across 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.

Download Now

Suggested citation: Abrams SA, Andres A, Byrd-Bredbenner C, Deierlein A, Eicher-Miller HA, Odoms-Young A, Fisher JO, Palacios C, Nevins J, Bahnfleth C, Higgins M, Raghavan R, Scinto-Madonich S, Butera G, Terry N, Obbagy J. Dietary Patterns Consumed During Pregnancy and Gestational Age at Birth: A Systematic Review. November 2024. U.S. Department of Agriculture, Food and Nutrition Service, Center for Nutrition Policy and Promotion, Nutrition Evidence Systematic Review. Available at: https://doi.org/10.52570/NESR.DGAC2025.SR26