Cord blood vitamin D status and neonatal outcomes in a birth cohort in Quebec, Canada.

Purpose: Some evidence suggests that low maternal vitamin D status adversely affects perinatal health but few studies have examined cord blood vitamin D status. This project aimed to determine the association between the cord blood concentration of 25-hydroxyvitamin D [25(OH)D] and neonatal outcomes.

Methods: A nested case-control study was conducted in Quebec City, Canada from 2005 to 2010. Included were 83 cases of low birthweight (LBW; <2500 g), 301 cases of small for gestational age (SGA; <10th percentile), 223 cases of preterm birth (PTB; <37 weeks' gestation), and 1027 controls. Levels of 25(OH)D were determined by chemiluminescence immunoassay. Adjusted odds ratios (OR) and 95 % confidence intervals (CI) were estimated with logistic regression.

Results: Cord blood [25(OH)D] <50 nmol/L was associated with a lower risk of LBW compared to [25(OH)D] ≥75 nmol/L (OR 0.47 95 % CI 0.23-0.97). For 25(OH)D levels 50-75 nmol/L, a significant association was not demonstrated (OR 0.58, 95 % CI 0.34-1.01). No significant associations were observed between [25(OH)D] and either SGA or PTB after adjustment.

Conclusions: Although our findings suggest that [25(OH)D] <50 nmol/L is associated with reduced risk of having a LBW infant, prenatal vitamin D recommendations require an examination of the literature that considers the full spectrum of maternal and neonatal outcomes.