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 D3 (25(OH)D3) concentrations. The fetal thymus size was measured by ultrasound in the third trimester. Neonatal 25(OH)D3 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) D3 concentrations were within the normal range in 48 (29.8%) mothers and 10 (13.1%) new-borns. A strong correlation between mid-pregnancy maternal and neonatal 25(OH)D3 concentration (r = 0.8, p < 0.001) was found. A significant linear correlation was observed between both, maternal and neonatal 25(OH)D3 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.