Objectives: The aim of this study was to compare the fetal thymus size measured in the second and third trimester of pregnancy in underweight women and women with normal weight. We hypothesized that the low maternal weight would affect the fetal thymus size, as maternal health and nutrition during pregnancy affect fetal development, including that of the fetal immune system.
Methods: The fetal thymus size was retrospectively assessed by determining the thymic-thoracic ratio in 77 pregnancies of underweight women (study group) and 85 pregnancies of women with normal weight (control group) between the 19th and 34th week of pregnancy. The anteroposterior thymic diameter and the intrathoracic mediastinal diameter were measured in the three-vessel view acquired from routine echocardiograms. The thymic-thoracic ratio was calculated by dividing the anteroposterior thymic diameter with the intrathoracic mediastinal diameter. Additionally, we compared the descriptive data between the two groups, such as gestational age at screening and at birth, birth weight, umbilical artery pH and APGAR-score after 5 min.
Results: The mean fetal thymic-thoracic ratio in underweight women was not significantly different to that in normal weight pregnancies (0.374 vs. 0.363). However, the average gestational age at birth, birth weight and APGAR-score at birth were lower in the group of underweight women.
Conclusions: There is no evidence that low maternal weight influences fetal thymus size during pregnancy. The differences we observed concerning fetal weight at birth, gestational age at delivery, APGAR-Score and birth weight percentile confirm the results of previous studies.
Keywords: BMI; fetal thymus size; thymus gland; ultrasound; underweight.
© 2025 the author(s), published by De Gruyter, Berlin/Boston.