Objectives: To evaluate the association between vitamin D status during pregnancy and total gestational weight gain (GWG), GWG rates and postpartum weight retention.
Methods: Prospective cohort of 163 women from Rio de Janeiro was followed at 5th-13th (baseline), 20th-26th, 30th-36th gestational weeks and at 30-62 days postpartum. Plasma 25-hydroxyvitamin D [25(OH)D] was evaluated during each trimester and was categorized as adequate (≥50 nmol/L) or inadequate (<50 nmol/L). GWG (kg) was calculated as the difference between the weight measured at baseline and 36th-42th gestational weeks. GWG rates (kg/week) were calculated between each visit. Postpartum weight retention (kg) was analysed as the difference between weights measured at 30-62 days postpartum and 5th-13th gestational weeks. Statistical analyses were performed using linear regression models that included interaction terms between vitamin D status and first trimester body mass index (BMI) (<25/≥25 kg/m2). Confounders were selected based on a directed acyclic graph.
Results: The prevalence of vitamin D inadequacy was 16.6%, 9.9% and 10.6% in the first, second and third trimesters, respectively. Overweight women with vitamin D inadequacy in the first (β = 3.70; 95% CI 0.09; 7.31, p-value = 0.045) and third trimester (β = 4.59, 95% CI 0.07; 9.10, p-value = 0.047) presented higher increases in total GWG than did women with vitamin D adequacy. This association was also observed between first trimester vitamin D status and GWG rates between visits 1 and 2 (β = 0.17; 95% CI 0.13; 0.36, p-value = 0.07).
Conclusions: There was an interaction effect of first trimester BMI (≥25 kg/m2) on the association between first and third trimester vitamin D status and GWG.