(P23-11-26) Identifying Determinants of Mother-Fetus Vitamin D Partitioning in Pregnant Adolescents at Risk of Vitamin D Deficiency

Objectives: Vitamin D is crucial for fetal development. The pregnant parent is the sole vitamin D source for the fetus, and concentrations of vitamin D prohormone, 25(OH)D, in maternal blood correlate strongly with fetal 25(OH)D. Maternal D deficiency can compromise child growth, bone mineral content and chronic illness susceptibility. The U.S. Dietary Guidelines deems vitamin D as a “nutrient of public health concern”, with high rates of insufficiency (25(OH)D < 20 ng/mL) in pregnant individuals. However, uncertainty remains regarding the benefits of raising maternal 25(OH)D in the context of D sufficiency. Furthermore, little is known regarding factors that influence fetomaternal D partitioning. This project sought to identify factors affecting the responsiveness of fetal 25(OH)D to maternal 25(OH)D using data from pregnant adolescents. The study cohort captured risk factors for D deficiency, including Black racial identification and obesity. Rates of mother-to-fetus D transfer were hypothesized to be higher in maternal D deficiency, meaning the correlation between maternal and fetal 25(OH)D would exhibit a steeper slope for D-deficient mothers compared to D-sufficient mothers.

Methods: Vitamin D metabolites 25(OH)D; 1,25(OH)₂D; and 24,25(OH)₂D were measured in serum from 51 pregnant adolescents (including 28 Black individuals) and in neonatal cord serum using liquid chromatography-tandem mass spectrometry. Data on race, pre-pregnancy body mass index, nutrient intake and other subject characteristics were collected via health records and self-report surveys.

Results: A positive correlation between maternal and cord 25(OH)D (ρ = 0.96, p < 0.001) was found, but multiple linear regression models showed the slope of this correlation was lower when maternal 25(OH)D was high (25(OH)D > 30 ng/mL, n = 20) (p < 0.001), indicating cord 25(OH)D increased at a slower rate in response to maternal 25(OH)D increases at these levels. Other factors associated with the slope of fetomaternal 25(OH)D correlations included Black racial identification.

Conclusions: Diminished increases in cord 25(OH)D at high maternal 25(OH)D concentrations indicate 25(OH)D may be partitioned less readily from the maternal to the fetal compartment at high maternal 25(OH)D concentrations.

Funding Sources: USDA 2011-03424