Morphometric indicators of the thymus mass in fetuses and early neonates

Objective: to identify reference values of thymus mass in fetuses and early neonates depending on their body mass. Materials and Methods. We analyzed 922 autopsy reports for fetuses of 18-42 weeks of gestation and neonates of the first 7 days of their life: Group I included those who died of infectious diseases (n=67); Group II comprised those who died of noncommunicable diseases (n=855). We examined the thymus mass and body mass, calculated the thymic index (TI). Spearman’s R was employed to evaluate the correlation. A polynomial regression model was constructed using the spline approximation method. Results. The data on the thymus mass are presented in the range of fetal and neonate body mass values from 300 g to 5,500 g. The thymus mass varied from 1.1 g to 1.48 g (for fetal mass of 300-500 g) to 12.36 g-15.09 g (for neonate body mass of 400-5,500 g). The organ mass increased with increasing gestational age, decreasing by day 3 of the newborn’s life. The median values of the thymic index for groups I and II 0.32 and 0.28 (p=0.2). Regardless of the pathology type, gestational age and life expectancy, the thymus mass correlated with the body mass (R=0.88; p<0.001). The dynamics of changes in the thymus mass (y) depending on the values of the decimal logarithm of the body mass (x) is described by the following polynomial regression equations: y=13.937x2-75.662x+104.47 for children of Group I and y=16.65x2-93.487x+133.56 for Group II. Conclusion. Reference values of the thymus mass in fetuses and neonates are presented depending on their body mass: we revealed that there is a strong direct correlation between the thymus mass and the body mass.