Maternal Serum 25-Hydroxyvitamin D Concentrations during Pregnancy and Infant Birthweight for Gestational Age: a Three-Cohort Study

BackgroundIn response to inconsistent findings, we investigated associations between maternal serum 25-hydroxyvitamin D [25(OH)D] concentrations and infant birthweight for gestational age (BW/GA), including potential effect modification by maternal race/ethnicity and infant sex. MethodsData from 2558 pregnant women were combined in a nested case-control study (preterm and term) sampled from three cohorts: the Omega study, the Pregnancy, Infection and Nutrition study, and the Pregnancy Outcomes and Community Health study. Maternal 25(OH)D concentrations were sampled at 4 to 29 weeks gestation (80% 14-26 weeks). BW/GA was modelled as sex and gestational age-specific birthweight z-scores. General linear regression models (adjusting for age, education, parity, pre-pregnancy body mass index, season at blood draw, and smoking) assessed 25(OH)D concentrations in relation to BW/GA. ResultsAmong non-Hispanic Black women, the positive association between 25(OH)D concentrations and BW/GA was of similar magnitude in pregnancies with female or male infants [beta ()=0.015, standard error (SE)=0.007, P=0.025; =0.018, SE=0.006, P=0.003, respectively]. Among non-Hispanic White women, 25(OH)D-BW/GA association was observed only with male infants, and the effect size was lower (=0.008, SE=0.003, P=0.02). ConclusionsMaternal serum concentrations of 25(OH)D in early and mid-pregnancy were positively associated with BW/GA among non-Hispanic Black male and female infants and non-Hispanic White male infants. Effect modification by race/ethnicity may be due, in part, to overall lower concentrations of 25(OH)D in non-Hispanic Blacks. Reasons for effect modification by infant sex remain unclear.