Bone mineral density during pregnancy in women participating in a randomized controlled trial of Vitamin D supplementation

Abstract

Background: Little is known about bone mineral density (BMD) during pregnancy. Advances in technology with lower radiation emissions by dual-energy X-ray absorptiometry instruments now permit the safe measurement of BMD during pregnancy. Objective: We evaluated maternal BMD during pregnancy as a function of vitamin D status in women of diverse racial/ethnic backgrounds. Design: A total of 301 women who underwent BMD measurements at 12–20 wk of gestation and again at 0–14 wk postpartum were included in this analysis. Women were a subset of subjects who were recruited for a randomized, controlled, double-blind trial of vitamin D supplementation in pregnancy (400, 2000, or 4000 IU/d). Results: Treatment had no significant effect on changes in BMD that occurred between 12–20 wk of gestation and 0–14 wk postpartum. Similarly, changes in spine and femoral neck bone mineral contents (BMCs) were not significantly different in the treatment groups. In addition, vitamin D inadequacy (serum 25-hydroxyvitamin D concentration, averaged across pregnancy,,50 nmol/L) was not associated with changes in BMD or BMC. There were significant racial/ethnic differences in spine BMD. African Americans lost more spine BMD than did Caucasians (20.04 6 0.04 compared with 20.02 6 0.04 g/cm2; P = 0.033). In addition, baseline obesity was associated with a greater loss of femoral neck BMD. The means 6 SDs of femoral neck BMD loss were 20.02 6 0.05 and 0.0 6 0.03 g/cm2 for groups with baseline body mass index (BMI; in kg/m2) $30 and,30, respectively. Conclusion: These findings do not support a dose effect of vitamin D supplementation on bone health and suggest that race/ethnicity and BMI play an important role in pregnancy bone health. This trial was registered at clinicaltrials.gov as NCT00292591.