Maternal plant-based diet during gestation and pregnancy outcomes

Purpose: We aimed to explore the association of vegetarian–vegan diets and pregnancy outcomes. Methods: A retrospective, web-based study conducted in 2017. Women who delivered < 4 years prior to enrolment where eligible to participate. Participants were allocated to 3 groups based on their self-reported diet during pregnancy: omnivores, vegetarians or vegans. Outcomes of interest including birthweight centile, small for gestational age (SGA), large for gestational age (LGA), preterm birth (PTB), maternal excessive weight gain (EWG) and gestational diabetes (GDM) were compared between the groups. Results: Overall, 1419 women of which 234 vegans (16.5%), 133 vegetarian (9.4%) and 1052 omnivores (74.1%) were included in final analysis. Maternal vegan diet during pregnancy was associated with a lower birth weight centile as compared to omnivores (42.6 ± 25.9 vs. 52.5 ± 27.0 P < 0.001), a greater adjusted odds ratio (aOR) for SGA (aOR = 1.74; 95% CI 1.05, 2.86) but not with the risk of LGA (aOR = 0.55; 95% CI 0.30, 1.00). Further adjustment for BMI showed similar but nonsignificant associations for SGA and LGA as compared to the omnivore group. Vegan diet was associated with lower risk for maternal EWG (aOR = 0.61; 95% CI 0.44, 0.86) and modest nonsignificant association with GDM (aOR = 0.54 95% CI 0.28, 1.03) which was further attenuated by adjustment for pre-pregnancy BMI. Maternal diet group was not associated with the risk of PTB or low birth weight. Conclusions: Maternal vegan diet is a protective factor from EWG but associated with a higher risk for SGA and lower birth weight centile. The association between vegan diet and fetal growth was mediated by maternal BMI.