OC24.07: Usefulness of measurement of the fetal thymus in the diagnosis of IUGR: a preliminary result

It is known that thymus is small in a growth-retarded baby. The purpose of this study is to assess the usefulness of the measurement of the fetal thymus in the diagnosis of intrauterine growth restriction (IUGR) of the fetus. The maximum transverse diameter of the thymus was measured on prenatal ultrasound in 20 fetuses with expected weight smaller than 10 percentile of their gestational age. We compared the diameter with the reference value from 376 normal fetuses. We divided the fetuses into two groups according to the prenatal ultrasound, Doppler, biophysical profile, and postnatal findings; normal or constitutionally small group and IUGR group. Small thymus was determined by two and three standard deviations (SD) compared with normal. We calculated the sensitivity, specificity, and predictive values (PPV and NPV) of the small thymus in the diagnosis of the IUGR. Using 2 SD as the cutoff value, 11 of 17 fetuses with small thymus were IUGR at birth. All three fetuses with normal thymus were normal or constitutionally small. Sensitivity, specificity, PPV, and NPV were 100%, 33%, 65%, and 100%. Using 3 SD, 10 of 12 fetuses with small thymus were IUGR. Six of eight fetuses with normal thymus were normal or constitutionally small. Sensitivity, specificity, PPV, and NPV were 83% 75%, 83%, and 75%. Small thymic diameter may be a useful finding in the diagnosis of IUGR on the prenatal ultrasound.