Vitamin D metabolite concentrations in umbilical cord blood serum and associations with clinical characteristics in a large prospective mother-infant cohort in Ireland

Vitamin D deficiency is widespread among mothers and neonates and quality clinical and analytical data are lacking. We used a CDC-accredited LC–MS/MS method to analyze vitamin D metabolites in cord sera from 1050 maternal-infant dyads in the prospective SCOPE Ireland Pregnancy and BASELINE Birth cohort studies, based in Cork, Ireland. The mean ± SD total 25(OH)D was 34.9 ± 18.1 nmol/L; 35% of cords (50% during winter) had 25(OH)D <25 nmol/L, 46% were <30 nmol/L and 80% were <50 nmol/L. In this predominantly white cohort, the main predictor of cord 25(OH)D [adj. mean difference in nmol/L (95% CI)] was summer delivery [19.2 (17.4, 20.9), P < 0.0001]. Maternal smoking during pregnancy (9% prevalence) was negatively associated (P < 0.002) with cord 25(OH)D [−4.83 (−7.9, −1.5) nmol/L]. There were no associations between cord 25(OH)D and birth weight or any anthropometric measures at birth. Despite the high prevalence of vitamin D deficiency at birth, there were no documented musculoskeletal complications during infancy, which was likely due to widespread supplementation with vitamin D. The mean ± SD concentration of 3-epi-25(OH)D₃, detectable in 99.4% of cord samples, was 3.3 ± 1.9 nmol/L. The proportion of 25(OH)D as 3-epi-25(OH)D₃ was 11.2%. Cord 3-epi-25(OH)D₃ concentrations were positively predicted by cord 25(OH)D₃ [0.101 (0.099, 0.103) nmol/L, P < 0.0001] and negatively by gestational age [−0.104 (−0.131, −0.076) nmol/L, P < 0.0001] and maternal age [−0.010 (−0.019, −0.001) nmol/L, P < 0.05]. 25(OH)D₂ was detected in 98% of cord sera (mean ± SD; 2.2 ± 1.9 nmol/L) despite low antenatal consumption of vitamin D₂ supplements. In conclusion, these first CDC-accredited data of vitamin D metabolites in umbilical cord blood emphasise the high risk of very low vitamin D status in infants born to un-supplemented mothers. Experimental data to define maternal vitamin D requirements for prevention of neonatal deficiency at high latitude are required.