Prevalence and predictors of vitamin D deficiency based on maternal mid-gestation and neonatal cord bloods: The Generation R Study

•Vitamin D deficiency (defined as less than 25mol/L) was identified in 26% of pregnant women at midgestation (∼20 weeks) in the mothers of the Dutch Generation R Study.•Vitamin D deficiency was found in 46% of the offspring when assessed in cord blood.•Based on both midgestation and cord blood sample, 21% of the mother-infant pairs had persistent vitamin D deficiency.•Persistent vitamin D deficiency in mother-infant pairs was strongly associated with non-European ancestry and spring birth. Population-based studies have confirmed that the prevalence of vitamin D deficiency is substantial in many societies, and is of particular concern in pregnant women. Vitamin D deficiency during pregnancy is associated with a wide range of adverse maternal and offspring health outcomes. To date, studies of vitamin D deficiency during pregnancy have focused on measurements at one or two time points in isolation. We examined both midgestation and cord blood 25 hydroxyvitamin D (25OHD) concentration and explored the prevalence and correlates of vitamin D deficiency in a large ethnically diverse cohort of pregnant women and their infants in the Netherlands. This study was embedded in the Generation R Study, a population-based prospective cohort from fetal life onwards in Rotterdam, The Netherlands. Using a highly sensitive tandem mass spectroscopy-based assay, we measured 25OHD in 7256 midgestation samples (mean gestation 20.6 weeks) and 5023 neonatal cord blood samples (mean gestation 40.0 weeks). Using a conservative threshold of less than 25nmol/L to define vitamin D deficiency, we examined the prevalence and socio-demographic correlates of vitamin D deficiency in mothers and infants. We also derived a measure of vitamin D deficiency based on the two time points in order to explore persistent vitamin D deficiency in mother-infant pairs. The prevalence of vitamin D deficiency at midgestation was 26%, while in neonates 46% were deficient. 21% of the mother-infant pairs had persistent vitamin D deficiency (i.e., deficient in maternal and cord samples) and an additional 29% were vitamin D deficient in one of the two samples only. Persistent vitamin D deficiency was strongly associated with non-European ancestry and spring birth. A sizeable proportion of women and their neonatal offspring in the Generation R cohort were vitamin D deficient. In light of the large body of evidence linking vitamin D deficiency with adverse health outcomes for pregnant women and their offspring, ou