Park H, et al. - In this study, researchers planned to further explore the placental vitamin D metabolism and its role in modulating maternal circulating vitamin D metabolites during pregnancy. They identified numerous associations of many of the placental biomarkers of vitamin D metabolism with circulating vitamin D metabolites among pregnant women [including a CYP27B1–associated increase in 1,25(OH)2D3] and the evidence of trophoblast production and secretion of vitamin D metabolites, especially 25(OH)D3. This suggested an active role of placenta in modulating the vitamin D metabolite profile in maternal circulation in human pregnancy.