Prenatal Ultrasound Findings and Chromosomal Outcomes of Pregnancies with Mosaic Embryo Transfer.

Background: To investigate prenatal ultrasound findings and the chromosomal outcomes of mosaic embryo transfer.

Methods: This retrospective study was conducted on pregnant women who underwent mosaic embryo transfer following blastocyst-stage preimplantation genetic testing for aneuploidy (PGT-A) at CHA Gangnam Medical Center from January 2021 to July 2024. Trophectoderm biopsy specimens were collected using standard protocols, and next-generation sequencing profiles were defined as mosaics when displaying copy number counts in the 20-80% range. The results of the PGT-A, the amniocentesis results, the findings of prenatal ultrasounds, and the pregnancy outcomes were analyzed.

Results: A total of 88 mosaic embryos were transferred, of which 77 embryos were successfully implanted. Sixty-seven embryo-maintained pregnancies went beyond 11 weeks (87.0%), all among 58 patients with singleton pregnancies. The chaotic subtype showed the lowest ongoing pregnancy rate, and high-level mosaicism was less frequent in the ongoing group, compared to the total study group and the successful implantation group. Amniocentesis was performed on 33 mothers (56.9%), revealing two cases with abnormal findings that did not correlate with the PGT-A results. Two cases showed abnormalities in the second trimester detailed ultrasound, and both subsequently demonstrated normal findings in the third trimester and after birth. The average gestational age at birth was 38.4 weeks, and the average birth weight was 3313 g. No congenital anomalies were detected in 16 postnatal cases.

Conclusions: Our study indicated that mosaic embryos can develop into euploid healthy infants with various levels or types of mosaicism, although the postnatal follow-up data are limited. This study is invaluable for counseling clinical results after mosaic embryo transfer, reassuring that, if patients do not have euploid embryos available, mosaic embryos can also be a viable option for transfer.