Maternal Serum Levels of Vitamin D and Foetal Bone Development

Abstract

Background: Rickets disease is a well-known example of the importance of vitamin D for optimal bone health during growth. Pregnant woman often have vitamin D deficiency. However, it is not clear whether maternal vitamin D influence their offspring’s bone-health, because results from different studies are conflicting. Therefore we wanted to study whether low maternal serum levels of 25-hydroxyvitamin D (25(OH)D) is associated with reduced foetal bone size and altered shape. Methods: In this prospective cohort study, 401 healthy, pregnant women aged 20-43 years were recruited in 2008-2009 at Mercy Hospital for Woman, Melbourne, Australia and 72 of them had serum levels of 25(OH)D measured at 28 weeks gestation. Foetal femur length (FL), distal femoral metaphysal cross sectional area (CSA), splaying index (distal CSA/FL) and femur volume (FV) were measured using 2D and 3D ultrasound at 20 and 30 weeks gestation. Associations between maternal 25(OH)D and z-scores of the foetal femur measurements were tested using Pearson’s correlation and linear regression analysis, and the proportion of explained variance was estimated from R2 . Results: At 20 weeks gestation, there was no significant correlation between maternal 25(OH)D and foetal femur z-scores (all p ≥ 0.10). At 30 weeks gestation, there was an inverse correlation of maternal 25(OH)D with foetal FL and FV, but not with other femoral z-scores. Each SD lower 25(OH)D, was associated with 0.41 higher FL z-score (p < 0.001) and 0.27 higher FV z-score (p = 0.030). These associations remained after adjustment for maternal body mass index, height, smoking, parity and ethnicity. Maternal 25(OH)D explained 16.5% of the variance in FL and 7.3% of the variance in FV. Conclusion: The inverse associations of 25(OH)D with FL and FV are surprising and challenging to explain. More research is needed to clarify the influence of maternal vitamin D on foetal bone development.