In vitro fertilization pregnancy may cause fetal thymic volume involution: A case-control study.

Background: The effect of modern infertility treatment modalities on fetal thymic volume has not been well known.

Objective: 3-dimensional (3D) fetal thymus volumes of 18-24 wk in vitro fertilization (IVF) pregnancies and spontaneous pregnancy cases were compared.

Materials and methods: 135 cases were evaluated in this prospective case-control study. The study was conducted between July 2019 and July 2020 at a university hospital in Trabzon, Turkey. Fetal thymus volume was calculated in the pregnant cases included in the study with the help of the virtual organ computer-assisted analysis system included in the advanced ultrasonography system. The fetal thymus volumes were compared between pregnant women with IVF and spontaneous pregnant women.

Results: The fetal thymus size was significantly lower in the IVF pregnancy group than in spontaneous pregnancy cases (p $<$ 0.001). It was found that the fetal complications, such as non-reassuring fetal health status and requirement for neonatal intensive care, were higher in cases who became pregnant after IVF treatment. It was also found that the rate of any pregnancy complication was significantly higher in IVF pregnancy group (p = 0.02).

Conclusion: In light of these results, it may be concluded that small fetal thymus size may be another fetal complication of IVF pregnancies.