Association between a Periconception Healthy Plant-Based Diet and Adverse Pregnancy Outcomes

BACKGROUND: Plant-based diets are increasingly popular and may improve cardiometabolic health, but their association with adverse pregnancy outcomes (APOs) is unclear, and dietary patterns are influenced by food access. OBJECTIVES: We investigated whether adherence to plant-based dietary patterns was associated with APOs and whether the association varied by neighborhood food access. METHODS: This is a secondary analysis using data from the Nulliparous Pregnancy Outcomes Study-Monitoring Mothers-to-Be cohort. Diet scores for the newer Healthy Plant-Based Diet Index (hPDI) and more established Dietary Approaches to Stop Hypertension (DASH) were derived from first-trimester Block Food Frequency Questionnaires and assessed in tertiles (T1 = "low," T3 = "high"). APOs included hypertensive disorders of pregnancy (HDP), gestational diabetes mellitus (GDM), preterm birth (PTB), small for gestational age (SGA), large for gestational age (LGA), and stillbirth. Modified Poisson regression models were used, adjusting for age, income, education, and health insurance. RESULTS: Among 7981 nulliparous individuals, higher hPDI scores were associated with lower risk of HDP [T3 compared with T1: adjusted risk ratio (aRR): 0.77; 95% confidence interval (CI): 0.64, 0.92; T2 compared with T1 aRR: 0.82; 95% CI: 0.70, 0.97] and GDM (T3 compared with T1: aRR: 0.55; 95% CI: 0.39, 0.76; T2 compared with T1: aRR: 0.71; 95% CI: 0.54, 0.95). Higher DASH scores were associated with lower risk of HDP (T3 compared with T1: aRR 0.83; 95% CI: 0.70, 0.98) and GDM, albeit for the second tertile only (T2 compared with T1: aRR 0.69; 95% CI: 0.52, 0.90). Neither diet was associated with PTB, SGA, or LGA. The frequency of low food access decreased across tertiles for both the hPDI and DASH (P < 0.05), but the associations between diet and APOs did not vary by food access (P > 0.05). CONCLUSIONS: A healthy plant-based diet in early pregnancy was associated with a lower risk of developing HDP and GDM in nulliparous individuals, which was similar to a DASH diet.