Dynamics of Vitamin D Metabolism in Maternal-Fetal Dyads.

Metabolites of vitamin D in maternal-neonatal dyads remain relatively unexplored. The goal of this study was to evaluate concentrations of 25(OH)D3, 24,25(OH)2D3, and 3-epi-25(OH)D3 in maternal-infant pairs at delivery.Serum samples of maternal and infant cord blood were collected on 131 mother-infant pairs at delivery. Vitamin D metabolites were analyzed in triplicate using liquid chromatography-tandem mass spectrometry. Statistical analysis was conducted using the Fisher exact test, Wilcoxon rank sum test, and Spearman correlation coefficients.Mean 25(OH)D3 concentrations in maternal and cord blood were 32.9 and 18.5 ng/mL, respectively; mean maternal and cord 24,25(OH)2D3 were 2.0 versus 1.1 ng/mL, respectively. Absolute concentrations of 3-epi-25(OH)D3 were similar in maternal and cord samples (2.4 vs 2.2 ng/mL), whereas the proportion of the total 25(OH)D as the 3-epimer was 6.5% in maternal samples and 10.5% in cord samples. This suggests that the fetus contributes significantly to 3-epi-25(OH)D3 production. In contrast, the ratio of 25(OH)D3:24,25(OH)2D3 was identical in maternal and cord samples (18.5) suggesting equivalent CYP24A1 activity in mother and fetus. Maternal and cord metabolite levels were highly correlated (r = 0.78, 0.90, 0.89 for 25(OH)D3, 24,25(OH)2D3, and 3-epi-25(OH)D3, respectively, P = 0.001 for all). Serum concentrations of all metabolites were lower in nonwhite infants compared with white infants. Maternal and cord concentrations of 25(OH)D3 were positively associated with birth weight (r = 0.21, P = 0.02; r = 0.25, P = 0.003, respectively).This data suggests that although maternal and cord concentrations of vitamin D metabolites are highly correlated, regulation of specific vitamin D metabolites in the mother and the neonate may be mediated independently.