Association of plant-based diet with the risk of large-for-gestational-age birth in women with gestational diabetes mellitus

The distribution of dietary macronutrients is critical for blood glucose management and adverse birth outcomes among pregnant women with gestational diabetes mellitus (GDM); however, the relationship between plant-based food intake and the risk of large-for- gestational-age (LGA) birth is unclear. Here, based on a large-scale birth cohort, we aim to investigate the prospective association between plant-based diet intake and the risk of LGA birth in pregnant women with GDM. We included 1768 GDM participants and assessed dietary plant-based diet patterns by constructing plant-based diet index (PDI), healthy plant-based diet index (hPDI) and unhealthy plant-based diet index (uPDI) using data collected from food frequency questionnaires (FFQ). LGA were defined as gender- and gestational age-adjusted birth weight of newborns greater than 90th percentile. We found that individuals in the highest quartile of uPDI had a significantly higher risk of LGA compared to those in the lowest quartile (OR :1.62, 95% CI: 1.02 to 2.62, p = 0.05), after adjusting for potential confounding factors. Moreover, the dose-response analysis indicated a significant nonlinear relationship, with the risk of LGA increasing as uPDI rose from the first to the second quartile (OR: 1.74, 95% CI: 1.06 to 2.88, p = 0.03) and then plateauing upon reaching the third quartile (OR: 2.00, 95% CI: 1.27 to 3.21, p < 0.01). The sensitivity analyses showed that this association was generally robust across different adjustment models, but was attenuated by further adjustment for glycated hemoglobin A1c (HbA1c), which indicated potential mediation roles of HbA1c between unhealthy plant-based diets and LGA risk. This study suggests that unhealthy plant food intake is a potential risk factor for LGA among pregnant women with GDM. The quality of plant-based foods should be considered when promoting plant-based dietary patterns.