Objective: The purpose of this study was to determine whether the size of the thymus is different in male and female fetuses.
Methods: In this prospective study, the transverse diameter and perimeter of the thymus were measured in healthy fetuses between 24 and 37 weeks' gestation. The means of the study variables from male and female fetuses were compared by the Student t test, and the relationships between the transverse diameter and perimeter of the thymus and gestational age and other common fetal biometric parameters were determined by linear regression modeling.
Results: No differences were noted between male and female fetuses for the means of the study variables. After the relationship between the transverse diameter and perimeter of the thymus and gestational age was confirmed (R(2) = 0.8 and 0.75, respectively; both P < .01), the 95% confidence interval-predicted changes were calculated, and the scatterplots of the measurements suggested that sex did not affect the size of the thymus. Bland-Altman plots were used to analyze intraobserver variability and showed good agreement for both of these thymic measurements for male and female fetuses.
Conclusions: These results suggest that fetal sex does not affect the size of the thymus and, together with previous reports, support the hypothesis that a quantitative reduction in fetal thymus size could serve as an indirect marker of abnormal thymopoiesis and congenital thymic insufficiency.