Fetal thymus size evaluation using two-dimensional ultrasound in co-relation to fetal biometry as a sensitive parameter change in pregnancies complicated with fetal growth restriction (FGR)

Objective: Fetal thymus size evaluation through measuring its ultrasonographic maximum transverse diameter, in relation to fetal biometry changes in pregnancies complicated with FGR. Methods: Our study included 66 singleton pregnancies with intact membranes, aged (18 to 40 y) between 28 and 36 weeks of gestation with FGR,Patients with fetal or maternal infections, chromosomal or fetal congenital anomalies, or IUFD and patients start labor were excluded. All patientsunderwentultrasound evaluation weekly during the third trimester after history taking; examination and lab
investigation were performed, where measurements of themaximum transverse diameter of the fetal thymus and fetal biometry (BPD percentile,FL percentile, AC percentile,EFW percentile,and Single deepest vertical pocket) were obtained. The small thymus was defined as a thymus perimeter ≤ 5th percentile according to a fetal thymus nomogram, then Patients were classified into 2 groupsaccording to whether they had a small transverse thymus diameter (< 5th %) or
normal transverse thymus diameter (> 5th %).The co-relation between fetal thymus size, obstetric history and fetal biometry changes by ultrasonography were performed. Results: The sixty-six FGR pregnancies were classified to 55 patients with thymus diameter less than 5th percentile and 11 patients with thymus diameter more than 5th percentile. The co-relation between thymus diameter less and more than 5th percentile and obstetric history showed that no statistically significant difference as regarding history of abortion, history of stillbirth, history of preterm labor and
history of IUGR but there was statistically significant difference as regarding gestational age (GA) mean at enrollment (32.04 ± 2.7 vs. 36.5 ± 1.04) meaning IUGR fetuses with a thymus diameter <5th % presented lower GA at enrollment. The correlation between thymus diameter and fetal biometry shows a highly significant positive correlation between thymus transverse diameter and FL, AC, EFW, and AF vertical pocket but non-significant correlation as regards
BPD in all cases of both groups. The comparison between thymus diameters less and more than 5th percentile in relation to fetal ultrasonic biometry showed that no statistically significant difference as regarding BPD mean percentile and FL mean percentile, on other hand, AC and EFW mean percentiles were statistically significantly higher among IUGR fetuses with normal thymus diameter (>5th percentile) [3.2 ± 2.7 vs. 6.6 ± 2.2 & 3.06 ± 2.6 vs. 6.09 ± 2.5]. 90.91% of IUGR fetuses with normal thymus diameter (>5th percentile) have adequate amniotic fluid as estimated by single deepest vertical pocket versus 34.55% of IUGR fetuses with thymus diameter <5th percentile with a statistically significant difference. All IUGR fetuses with oligohydramnios (n=20) had small thymus < 5th %. Conclusion: There is a highlypositive correlation between thymus transversediameter and AC, EFW, and AF vertical pocket inpregnancies complicated with FGR.