First trimester vitamin D, vitamin D binding protein, and subsequent preeclampsia

Abstract

Previous studies report an association between vitamin D deficiency and hypertension, including the pregnancy-specific disorder preeclampsia. Circulating vitamin D is almost entirely bound to vitamin D binding protein, which increases 2-fold during pregnancy and previous studies have not examined vitamin D binding protein or free vitamin D levels. We performed a nested case-control study within the Massachusetts General Hospital Obstetric Maternal Study, measuring first trimester total 25-hydroxyvitamin D (25[OH]D) and vitamin D binding protein and calculating free 25(OH)D levels. We compared these levels from pregnancies complicated by subsequent preeclampsia (cases, n=39) with those from normotensive pregnancies (controls, n=131). First trimester total 25(OH)D levels were similar in cases and controls (27.4±1.9 versus 28.8±0.80 ng/mL; P=0.435). Despite an association between higher first trimester blood pressures and subsequent preeclampsia, first trimester total 25(OH)D was not associated with first trimester systolic (r=0.11; P=0.16) or diastolic blood pressures (r=0.03; P=0.72). Although there was a trend toward increased risk of preeclampsia with 25(OH)D levels <15 ng/mL (odds ratio: 2.5 [95% CI: 0.89 to 6.90]), this was attenuated after adjustment for body mass index and other covariates (odds ratio: 1.35 [95% CI: 0.40 to 4.50]). First trimester vitamin D binding protein and free 25(OH)D levels were similar in cases and controls and were not associated with first trimester blood pressures. These data suggest that first trimester total and free 25(OH)D levels are not independently associated with first trimester blood pressure or subsequent preeclampsia.

Figure 1

First trimester serum 25-hydroxyvitamin D concentrations in women who remained normotensive (n=131) and women who developed subsequent preeclampsia (n=39). First trimester 25(OH)D levels were not significantly different in who developed subsequent preeclampsia compared to normotensive women (mean ± standard error=27.4 ± 1.9 vs. 28.8 ± 0.80, p=0.435). To express total 25(OH)D levels (ng/ml) in nmol/L, multiply by conversion factor 2.496.

Figure 2

First trimester serum levels of Total and Free 25(OH)D in women who remained normotensive (N=131) and women who developed subsequent preeclampsia (N=39). Levels of Free 25(OH)D did not differ significantly between groups (p=0.80). To express total 25(OH)D levels (ng/ml) in nmol/L, multiply by conversion factor 2.496.

Figure 3

Relationship between 25-hydroxyvitamin D, Vitamin D Binding Protein, and Body Mass Index (BMI). 25(OH)D levels were positively associated with VDBP levels and inversely associated with body mass index (kg/m²). To express total 25(OH)D levels (ng/ml) in nmol/L, multiply by conversion factor 2.496.

Figure 4

Levels of Total and Free 25(OH)D by Obesity. Subjects who were obese (body mass index ≥30 kg/m², n=31) had lower levels of total 25(OH)D compared to non-obese subjects (n=137, p=0.005), but free 25(OH)D levels did not differ (p=0.691). To express total 25(OH)D levels (ng/ml) in nmol/L, multiply by conversion factor 2.496.