Vitamin D deficiency in pregnancy may affect fetal thymus development

Objectives: The aim of our study was to evaluate the association of vitamin D deficiency (VDD) during pregnancy with thymus size in full-term fetuses. Material and methods: In this prospective study, we evaluated mid-pregnancy serum 25-hydroxyvitamin D-3 (25(OH)D-3) concentrations. The fetal thymus size was measured by ultrasound in the third trimester. Neonatal 25(OH)D-3 levels were evaluated by umbilical cord blood sampling. Correlation of maternal and neonatal vitamin D levels and association between thymus size and both, maternal and neonatal vitamin D concentrations were investigated. Results: Serum 25(OH)D-3 concentrations were within the normal range in 48 (29.8%) mothers and 10 (13.1%) newborns. A strong correlation between mid-pregnancy maternal and neonatal 25(OH)D-3 concentration (r = 0.8, p < 0.001) was found. A significant linear correlation was observed between both, maternal and neonatal 25(OH)D-3 concentrations and thymus perimeter length (r = 0.45, p = 0.04 and r = 0.43, p < 0.01, respectively). Both, maternal and fetal VDDs were associated with decreased thymus perimeter (p = 0.04, p = 0.03). Conclusions: Vitamin D deficiency during pregnancy may be associated with smaller fetal thymus. Our data suggest that VDD in pregnancy may lead to systemic inflammatory response in the fetus.