<b><i>Background:</i></b> High prevalence of vitamin D deficiency in pregnancy is recorded. <b><i>Aim:</i></b> To establish determinants of postpartum 25-hydroxyvitamin D (25(OH)D) levels on mothers and offspring. <b><i>Methods:</i></b> 25(OH)D level was measured in cord blood and maternal blood collected ≤3 weeks postpartum. Maternal socioeconomic status, vitamin D intake, sun exposure during pregnancy and maternal and neonatal fat mass (FM; dual X-ray absorptiometry) were assessed within 3 weeks postpartum. <b><i>Results:</i></b> A total of 174 mother-offspring pairs were enrolled. Maternal 25(OH)D <20 ng/ml was seen in 32 (51%) of summer and 82 (74%) of winter deliveries. Women with 25(OH)D <20 ng/ml had a 2-fold lower percentage of vitamin D intake of ≥800 IU/day than women with 25(OH)D ≥20 ng/ml (p = 0.02). FM (%) was comparable between groups (p > 0.05). Multiple regression analysis revealed the delivery season, prenatal vitamin D intake ≥800 IU/day and duration of supplementation to be the determinants of maternal 25(OH)D level (R² = 0.26, p < 0.001). Maternal 25(OH)D level, season of birth and duration of maternal supplementation explained 83% of the variance in cord blood 25(OH)D level (R² = 0.83, p < 0.001). <b><i>Conclusions:</i></b> The key determinants of higher maternal vitamin D status were the summer-autumn season of delivery and prenatal use of ≥800 IU/day of vitamin D. The cord blood 25(OH)D level was mainly determined by maternal 25(OH)D level and season of birth.