maternal vitamin d concentration in mid-pregnancy and its effect on fetal thymus size: a report from a tertiary center in iran

Background & objective: the thymus gland significantly affects fetal immune system maturation. additionally, there is a linear association between thymus gland size and its performance. given the high prevalence of vitamin d deficiency in iran and scarce studies with conflicting results, subjecting maternal vitamin d concentration effect on fetal thymus, we decided to investigate maternal vitamin d concentration and its relation to fetal thymus size in mid-gestation. this study also aimed to generate a race-specific reference range.materials & methods: we performed a cross-sectional study of ultrasound measurements of the fetal thymus at 18-22 weeks of gestational age in 94 pregnant women and its correlation with maternal serum vitamin d levels from may to july 2021 at the tertiary center of imam khomeini hospital in tehran, iran.results: the mean values of thymus perimeter, thymus-thoracic ratio, thymus transverse diameter, and thymus area in all participants were 4.18±0.56 cm, 0.37±0.04, 1.56±0.21 cm, and 1.11±0.76 cm2, respectively. there was a trend toward decreased thymus perimeter and transverse thymus diameter with decreasing level of maternal vitamin d. there was also a significant correlation between thymus perimeter and transverse thymus diameter with fetal biometric indices and gestational age. furthermore, a significant correlation was observed between the thymus perimeter and transverse thymus diameter.conclusion: we generated a race-specific nomogram for fetal thymus size in iranian pregnant women. moreover, the observed trend toward decreased fetal thymus size with decreasing maternal vitamin d levels requires further prospective investigations. a high prevalence of vitamin d deficiency and low compliance with daily vitamin d intake during pregnancy was also shown, which requires a solution.