Maternal Dietary Patterns, Socioeconomic Conditions, and Birth Outcomes in the MAMI-MED and Piccolipiù Italian Birth Cohorts

Background/Objectives: Maternal diet during pregnancy may influence neonatal outcomes, but dietary behaviours are socially patterned and were measured differently across cohorts. We therefore evaluated whether cohort-specific, partially harmonized maternal dietary patterns were associated with adverse birth outcomes after accounting for maternal and socioeconomic characteristics in two Italian birth cohorts. Methods: We analyzed 3234 mother–infant dyads from Piccolipiù (2011–2015) and 1564 from MAMI-MED (2020–ongoing). Maternal diet was captured by cohort-specific food questionnaires and grouped into food categories. Principal component analysis identified dietary patterns; pattern scores were categorized into tertiles and combined into five joint-adherence profiles. Logistic regression estimated odds ratios (OR) for preterm birth (PTB, <37 weeks), low birth weight (LBW, ≤2500 g), macrosomia (≥4000 g), and small/large for gestational age (SGA/LGA), with progressive adjustment for maternal age, pre-pregnancy body mass index (BMI), education, employment, and (Piccolipiù) income. Results: Two comparable patterns emerged in both cohorts: Western (processed foods, fried items, snacks/sweets, sugar-sweetened beverages) and Prudent (fruit, vegetables, fish, whole grains/yogurt). Western adherence was more common among younger women and those with disadvantage, whereas Prudent adherence tracked higher education, employment and income. After full adjustment, dietary profiles were not consistently associated with PTB, SGA or LGA in either cohort. In Piccolipiù, preferential Prudent adherence was associated with lower odds of LBW (OR 0.49; 95% CI 0.24–0.92) and higher odds of macrosomia (OR 1.56; 95% CI 1.06–2.30). Across cohorts, higher pre-pregnancy BMI predicted macrosomia/LGA, while lower education increased the probability of PTB and LBW. Conclusions: Across two Italian birth cohorts, maternal dietary patterns were socially stratified, whereas pre-pregnancy BMI and maternal education were more consistently associated with birth outcomes than dietary-pattern adherence per se.