LAUSR

To determine predictors of 25-hydroxyvitamin D3 (25(OH)D3) concentrations (25th, 50th, and 75th percentiles) in the third trimester of pregnancy. Data on sociodemographic, obstetric, lifestyle and pregnancy characteristics, including serum 25(OH)D3 and retinol, were collected among 448 pregnant women who participated in the Maternal and Child Health and Nutrition in Acre, Brazil (MINA-Brazil Study) in Cruzeiro do Sul, Brazilian Amazon (latitude 7°S). Simultaneous-quantile regression was fitted to prospectively assess predictors at the 25th, 50th and 75th percentiles of 25(OH)D3 concentrations. In the third trimester, 25(OH)D3 <50 nmol/L was observed in 26% of pregnant women. Exposure to the Amazonian dry season during follow-up and vitamin D status ≥75 nmol/L in the second trimester of pregnancy were positively associated with 25(OH)D3 concentrations in the third trimester. Pregnant women who were the main providers of family income presented lower 25(OH)D3 concentrations (50th and 75th percentiles: −15 nmol/L, 95%CI −24; −3, p = 0.02, and −22 nmol/L, 95%CI −36; −7, p = 0.004, respectively), as well as those with sustained vitamin A insufficiency (25th and 50th percentiles: −27 nmol/L, 95%CI −40; −15, p < 0.001, and −17 nmol/L, 95%CI −33; −1, p = 0.04, respectively). Sun protection practices had a smaller negative impact on 25(OH)D3, restricted to participants whose concentrations were at the 25th percentile of the distribution. Seasonality and vitamin A status were important predictors of 25(OH)D3 concentrations in the third trimester. Adequate exposure to sunlight and dietary sources of vitamin A within safe intake levels may help ensuring a good nutritional status of vitamin D during pregnancy.