Accumulation of Cleavage-Stage Embryos by Vitrification may Compromise Embryonic Developmental Potential in Preimplantation Genetic Testing

It was suggested that the embryo pooling was an alternative for patients with insufficient number of embryos for preimplantation genetic testing (PGT) in a single ovarian stimulation cycle. However, limited study noticed whether it is an efficient strategy to pool cleavage-stage embryos by vitrification. This study included 71 cycles with vitrified-warmed and fresh embryos simultaneously for PGT between May 2016 and May 2021. The embryos from the same patients were split into two groups based on the origin: warming group and fresh group. Embryo development, sequencing results, clinical and neonatal outcomes were compared. The results showed that the rate of high-quality embryos in the warming group was significantly higher than that in the fresh group (64.53% versus 52.61%, P = 0.011); however, the available blastocyst rate in this group was significantly lower than that in the fresh group (47.29% versus 57.83%, P = 0.026). There were 96 and 144 blastocysts that underwent trophectoderm (TE) biopsy in warming and fresh groups, respectively. The high-quality blastocyst rate was significantly lower in the warming group compared to the fresh group (57.29% versus 70.14%, P = 0.041). The rates of genetic transferable blastocyst were comparable between the two groups ( P = 0.956). There were no statistical differences in terms of embryo implantation, clinical pregnancy, miscarriage rates, and neonatal outcomes between the two groups. In conclusion, this study demonstrated that the cleavage-stage embryo pooling strategy might be unfavorable for the maintenance of embryonic development potential. If not necessary, it is not recommended to pool cleavage-stage embryos for PGT.