Background: Nutrition plays a fundamental role in fetal growth and birth outcomes.

Objective: We synthesized effects of dietary interventions before or during pregnancy on neonatal and infant outcomes.

Design: Randomized controlled trials that assessed the whole diet or dietary components and neonatal or infant outcomes were included. Two authors independently identified articles to be included and assessed the methodologic quality. A meta-analysis was conducted separately for each outcome by using a random-effects model. Results were reported by dietary intervention as follows: 1) counseling, 2) food and fortified food products, or 3) a combination (counseling plus food) intervention, and 4) collectively for all dietary interventions. Results were subanalyzed by the nutrient of interest, country income, and BMI.

Results: Of 2326 abstracts screened, a total of 29 randomized controlled trials (31 publications) were included in this review. Food and fortified food products were effective in increasing birth weight [standardized mean difference (SMD): 0.27; 95% CI: 0.14, 0.40; P < 0.01] and reducing the incidence of low birth weight (SMD: −0.22; 95% CI: −0.37, −0.06; P < 0.01). All dietary interventions and those focused on macronutrient intake also increased birth weight (P < 0.01) and length (P < 0.05) and reduced the incidence of low birth weight (P < 0.01). Dietary interventions in low-income countries and underweight or nutritionally at-risk populations increased birth weight (P < 0.05) and reduced the incidence of low birth weight (P = 0.01). No effects were seen for the following other outcomes: placental weight, head circumference, macrosomia, Apgar score, small for gestational age, large for gestational age, and perinatal mortality.

Conclusion: Additional high-quality randomized controlled trials that test different dietary interventions are required to identify maternal diet intakes that optimize neonatal and infant outcomes.