Low maternal vitamin D status and fetal bone development: Cohort study

Recent findings suggest that maternal vitamin D insufficiency during pregnancy has consequences for the offspring's bone health in later life. To investigate whether maternal vitamin D insufficiency affects fetal femur growth in ways similar to those seen in childhood rickets and study the timing during gestation of any effect of maternal vitamin D status, we studied 424 pregnant women within a prospective longitudinal study of maternal nutrition and lifestyle before and during pregnancy (Southampton Women's Survey). Using high‐resolution 3D ultrasound, we measured fetal femur length and distal metaphyseal cross‐sectional area, together with the ratio of femoral metaphyseal cross‐sectional area to femur length (femoral splaying index). Lower maternal 25‐hydroxyvitamin vitamin D concentration was not related to fetal femur length but was associated with greater femoral metaphyseal cross‐sectional area and a higher femoral splaying index at 19 weeks' gestation [r = −0.16, 95% confidence interbal (CI) −0.25 to −0.06 and r = −0.17, 95% CI −0.26 to −0.07, respectively] and at 34 weeks' gestation (r = –0.10, 95% CI −0.20 to 0.00 and r = −0.11, 95% CI −0.21 to −0.01, respectively). Three groups of women were identified with 25‐hydroxyvitamin vitamin D concentrations that were sufficient/borderline (>50 nmol/L, 63.4%), insufficient (25 to 50 nmol/L, 30.7%), and deficient (≤25 nmol/L, 5.9%). Across these groups, the geometric mean femoral splaying indices at 19 weeks' gestation increased from 0.074 (sufficient/borderline) to 0.078 (insufficient) and 0.084 (deficient). Our observations suggest that maternal vitamin D insufficiency can influence fetal femoral development as early as 19 weeks' gestation. This suggests that measures to improve maternal vitamin D status should be instituted in early pregnancy. © 2010 American Society for Bone and Mineral Research