Objectives. This cross-sectional study primarily aimed to assess vitamin D adequacy in the third trimester of pregnancy using 25-hydroxyvitamin D (25(OH)D) and explore lifestyle characteristics (sun exposure index, diet, and economic indicators) associated with serum 25(OH)D. The secondary aim was to examine the relationship of serum 25(OH)D with birth weight and gestational age. Methods. Serum 25(OH)D was measured by chemiluminescent immunoassay in 150 pregnant women from Mumbai. Sun exposure index was computed. Dietary calcium, phytate: calcium ratio, and dietary phosphorus was calculated using the 24-hour diet recall method. Results. All women had 25(OH)D levels < 30.00 ng/ml. Multivariable linear regression showed that nonaffluent women had poorer 25(OH)D status than their affluent counterparts (β = - 0.20; P = 0.03). Higher sun exposure index was associated with higher 25(OH)D concentrations (β = 0.31; P < 0.001), which remained significant after controlling for covariates. At the bivariate level, mothers of infants weighing <2500 g had lower serum 25(OH)D concentrations compared to mothers whose infants weighed ≥ 2500 g (P = 0.02). This association became non-significant after controlling for covariates. Conclusions. Vitamin D deficiency was universally prevalent in the cohort studied. There is a need to develop culturally sensitive strategies for improving the 25(OH)D status.