THE ESTIMATED FREE CONCENTRATION OF CALCIDIOL IS HIGHER IN VENOUS CORD-BLOOD THAN IN MATERNAL BLOOD

The serum levels of calcidiol (25-hydroxy-vitamin D-3), calcitriol (1,25-dihydroxy-vitamin D-3), albumin and vitamin D-binding protein (DBP) were measured in venous cord blood and in maternal blood at delivery. These results were used to calculate the free concentrations of calcidiol and calcitriol in maternal and fetal blood. Fifty three women participated in the study. Seventeen of the participants were excluded from the calculations because their calcidiol levels were below the limit of detection (<5 nmoll(-1)). The estimated free concentration of calcidiol was on average 26% higher in cord serum than in maternal serum, the mean difference being 1.1 pmoll(-1) (p=0.001). The estimated free concentration of calcitriol, however, was 21% lower on the fetal side (p < 0.001). The difference was small, the mean value being 0.07 pmoll(-1). A strong positive association existed between the serum levels of free calcidiol (r = 0.82, p < 0.001) and free calcitriol (r = 0.83, p < 0.001) in maternal blood and cord blood.