Reproductive outcomes of mosaic embryo transfers in preimplantation genetic testing for structural rearrangement cycles: a retrospective cohort study.

PURPOSE: To study reproductive outcomes of transferring embryos with mosaic chromosomal aneuploidies unrelated to target loci in preimplantation genetic testing for structural rearrangement (PGT-SR). METHODS: A retrospective analysis of 1712 PGT-SR cycles (involving 1373 couples) from a single center was conducted. Comprehensive chromosomal analysis was performed on trophectoderm biopsy samples using whole-genome amplification combined with next-generation sequencing. Clinical outcomes after single embryo transfer, including clinical pregnancy rate, miscarriage rate, live birth rate, and ectopic pregnancy rate, were compared between mosaic embryo transfers and completely euploid embryo transfers. RESULTS: In PGT-SR cycles, euploid embryo transfers (1338 cycles) demonstrated a clinical pregnancy rate of 65.17%, live birth rate of 58.67%, miscarriage rate of 6.05%, and ectopic pregnancy rate of 0.45%, whereas mosaic embryo transfers (165 cycles) exhibited comparable outcomes with 58.18%, 54.55%, 3.64%, and 0%, respectively. The subgroup analysis by mosaic degree which revealed low-level mosaicism (20%-29% and 30%-49%) had outcomes similar to euploid embryos. High-level mosaicism (50%-69%) demonstrated significantly reduced clinical pregnancy (OR = 0.20, 95% CI 0.06-0.54) and live birth rates (OR = 0.20, 95% CI 0.06-0.56), though miscarriage remained comparable. No significant outcome variations were observed across chromosomal types. CONCLUSIONS: In PGT-SR cycles, embryos with low-level mosaicism (20%-49%) unrelated to target loci demonstrate equivalent clinical pregnancy and live birth outcomes to completely euploid embryos. Although high-level mosaicism (50%-69%) is likely associated with reduced live birth rates, these embryos still retain potential for healthy live births.