Placental uptake and metabolism of 25(OH)vitamin D determine its activity within the fetoplacental unit.

Pregnancy 25-hydroxyvitamin D [25(OH)D] concentrations are associated with maternal and fetal health outcomes. Using physiological human placental perfusion and villous explants, we investigate the role of the placenta in regulating the relationships between maternal 25(OH)D and fetal physiology. We demonstrate active placental uptake of 25(OH)D by endocytosis, placental metabolism of 25(OH)D into 24,25-dihydroxyvitamin D and active 1,25-dihydroxyvitamin D [1,25(OH)D], with subsequent release of these metabolites into both the maternal and fetal circulations.