Prognostic Value of Fetal Thymus Size in Intrauterine Growth Restriction

Objectives-Our aim was to evaluate the size of the fetal thymus by sonography in pregnancies with intrauterine growth restriction (IUGR) and to search for a possible relationship between a small fetal thymus and adverse perinatal outcomes. Methods-The transverse diameter of the fetal thymus was prospectively measured in 150 healthy and 143 IUGR fetuses between 24 and 40 weeks' gestation. The fetuses with IUGR were further divided according to normal or abnormal Doppler assessment of the umbilical and middle cerebral arteries and ductus venosus. Measurements were compared with reference ranges from controls. To determine which perinatal outcomes were independently associated with a small fetal thymus, a multivariate logistic regression analysis was performed. Results-Thymus size was significantly lower in IUGR fetuses compared to controls (P <.05). Among IUGR fetuses, thymus size was significantly smaller in IUGR fetuses with abnormal Doppler flow compared to normal flow (P <.05). A small thymus in IUGR fetuses was independently associated with early delivery (odds ratio [OR], 1.24; 95% confidence interval [CI], 1.05-1.49; P=.023), respiratory distress syndrome (OR, 1.36; 95% CI, 1.09-1.78; P=.005), early neonatal sepsis (OR, 1.65; 95% CI, 1.11-2.42; P=.001), and a longer stay in the neonatal intensive care unit (OR, 1.33; 95% CI, 1.08-1.71; P =.017). Conclusions-Intrauterine growth restriction is associated with fetal thymic involution, and a small fetal thymus is an early indicator of adverse perinatal outcomes in pregnancies complicated by IUGR.