Maternal and Neonatal Vitamin D Status at Preterm Delivery—A Cross-Sectional Study

Background: An optimal 25OHD level can prevent osteopenia of prematurity (bone health) and premature delivery (non-skeletal activity). Although maternal and fetal vitamin D (25OHD) levels correlate, data on preterm infants’ 25OHD status at birth are limited, with a well-recognized deficiency among term infants. Objectives: To evaluate maternal and neonatal 25OHD status at preterm birth and its determinants in a northern-latitude country, Poland. Design/Methods: Cross-sectional study between August 2015 and September 2016 investigating cord and maternal blood 25OHD levels at delivery in 69 pairs of mothers and newborns ≤ 32 6/7 weeks of gestation, and analyzing correlations between maternal and neonatal 25OHD levels and their influencing factors, with univariable and multivariable linear regression. Results: Median (IQR) 25OHD levels were 25 (16.6–34 ng/mL) in cord blood and 21.2 (15–29 ng/mL) in mothers and correlated positively (r = 0.69, p < 0.0001). 25OHD insufficiency was detected in 84.06% of mothers and 62.32% of newborns. Maternal 25OHD levels were higher in summertime delivery (p = 0.0008). The rate of vitamin D supplementation during pregnancy was 54.4%, increasing maternal (27 ng/mL vs. 16.7 ng/mL, p = 0.0006), cord blood (32.4 ng/mL vs. 17.4 ng/mL, p = 0.0005), and summer seasonal cord blood 25OHD levels (38.89 ng/mL vs. 25.5 ng/mL, p = 0.023), and the percentage of maternal (72.7% vs. 27.3%, p = 0.005) and neonatal 25OHD sufficiency (80% vs. 20%, p = 0.0021). Conclusions: Vitamin D insufficiency is common in mothers and their prematurely born infants at birth; vitamin D supplementation reverses the trend. To avoid inadequate supplementation in preterm newborns and in mothers at risk of preterm delivery, regular assessment of 25OHD levels should be considered.