Pregnancy in dark winters: implications for fetal bone growth?

Objective: To prospectively examine the prevalence of hypovitaminosis D in pregnancy and to correlate maternal and fetal vitamin D to fetal anthropometry.

Design: A prospective cohort study.

Setting: Tertiary referral maternity hospital.

Patient(s): Sixty pregnant women.

Intervention(s): Serum 25-hydroxyvitamin D (25OHD) was measured in early pregnancy, at 28 weeks, and in cord blood at delivery.

Main Outcome Measure(s): The prevalence of hypovitaminosis D and the relationship between fetal growth and serum 25OHD concentrations.

Result(s): Two subgroups were analyzed to examine results in the context of seasonal variation in 25OHD: a winter and a summer cohort. Fetal anthropometry was assessed at 20 and 34 weeks, and at delivery the neonatal anthropometry was recorded. There was a high prevalence of hypovitaminosis D ranging from 33% to 97%, with a marked seasonal variation. Fetal 25OHD concentrations correlated with all biometry at 20 weeks. In the winter cohort, a correlation was found between early pregnancy 25OHD and femur length at 20 weeks, and between 28-week 25OHD and femur length at 34 weeks. Infant length was shorter in those with early pregnancy 25OHD less than the median (52.1 vs. 53.6 cm).

Conclusion(s): The high prevalence of maternal hypovitaminosis D during winter months in northern latitudes may have detrimental effects on fetal skeletal growth.