CHANGES IN MATERNAL VITAMIN D STATUS THROUGHOUT PREGNANCY AND THE EFFECTS OF SUPPLEMENTATION

Abstract

BACKGROUND: Pregnant women make up a special population at increased risk for vitamin D insufficiency and deficiency. Maternal 25 hydroxyvitamin D (25(OH)D) status has implications for the health of the mother and fetus. Because blood lipids change during pregnancy, it may be important to measure not only 25(OH)D but also to ratio 24(OH)D to plasma triacylglycerol (TAG). METHODS: Blood samples were collected at enrollment (8-22 weeks gestation) and delivery from a mixed race population of pregnant women (n=299) living in the Kansas City metropolitan area at latitude 39°06' north. Plasma 25(OH)D was measured by enzyme immunoassay (EIA). TAG was measured by enzymatic hydrolysis assay. RESULTS: Rates of deficiency, insufficiency, sufficiency, and toxicity were 25.8%, 30.4%, 40.8% and 3.0% respectively at enrollment and 54.9%, 29.6%, 15.6% and 0% respectively at delivery. Mean 25(OH)D concentration of African American women at enrollment was 12.39 ± 2.94 ng/ml and 6.80 ± 3.20 ng/ml at delivery. Caucasian women had mean levels of 23.84 ± 3.80 ng/ml at enrollment and levels of 13.37 ± 3.36 ng/ml at delivery. Vitamin D levels of Caucasian women were significantly higher than African American women at both enrollment (p <0.00001) and delivery (p <0.0001). Maternal BMI was associated with lower 25(OH)D status at enrollment (p < 0.001) and delivery ( p = 0.018). Season of blood collection significantly affected 25(OH)D status at delivery (p < 0.001). Vitamin D supplementation was significantly associated with higher 25(OH)D status at delivery (p =0.033). Maternal concentration of TAG was not significantly related to 25(OH)D status at enrollment or delivery. CONCLUSION: Despite vitamin D supplementation, maternal 25(OH)D status decreased by 40% from 8-20 weeks gestation to infant delivery. The 40% increase in maternal plasma volume between 8 and 32 weeks gestation may influence 25(OH)D status at infant delivery.