Abstract
The thymus is a lymphoepithelial organ, and its morphometry is commonly utilized for surveillance of the immunological status of fetus and neonates. Many studies showed that fetal thymus size is used as a prognostic indicator for pregnancy-related disorders such as eclampsia, preterm labor, and gestational diabetes. The study aims to establish reference ranges of the normal fetal thymus size between 12 and 40 weeks of gestational age (GA). The study was conducted on 89 fetuses. They were dissected to capture the morphometry of thymus: transverse diameter, perimeter, and weight. Considering these parameters were dependent variables of GA and gestational weight (GW). Their relationship was studied by a multiple regression model. The best fit models in predicting thymic dimensions as a function of GA and GW were determined using regression analysis. Mean transverse diameter, perimeter, and thymus weight was 33.45 +/- 2.91 mm, 125.72 +/- 55.4 mm, and 3.078 +/- 3.06 g, respectively. They were increased throughout pregnancy as GA and GW advanced. The regression equation for a transverse diameter of the thymus as a function of GA was (0.303xGA-4.885, R-2=0.8196) and for the perimeter of the thymus was (1.0212xGA-15.24, R-2=0.8666). Reference ranges and baseline data of the normal fetal thymic dimensions between 12 and 40 weeks of GA have been established.