Generation of viable blastocysts from discarded human cleavage embryos

Background: By improving the culture systems, demonstrated that some discarded poor quality embryos can reach to blastocyst and are capable to implantation. Objective: This study investigated blastocyst developmental competence and euploidy status in human embryos that had been classed as too poor quality to transfer (ET) or cryopreserve at the cleavage stage. Materials and Methods: Embryos were divided into three groups. Group 1 (n=41) included good quality embryos from candidates of preimplantation genetic testing for aneuploidy (PGT-A). Groups II and III were the ‘rejected’ supernumerary embryos, defined as suboptimal for ET or vitrification after morphological examination, with embryos randomly divided between the groups. Group II embryos (n=31) were cultured up to the Day 3 cleavage stage, when they were biopsied and fixed. Group III embryos (n=27) were cultured up to the Day 5 blastocyst stage, when they were evaluated for morphology and chromosomal status. Chromosomal status in all groups was assessed by multi–color fluorescence in-situ hybridization (FISH) for chromosomes 13, 18, 21, X and Y. Results: Euploidy rates in Groups I, II and III were 56.1%, 38.7%, and 55.5%, respectively. Among the blastocysts that developed from ‘rejected’ embryos, 59.3% were classed as good quality. The most frequent chromosomal aneuploidy was related to the sex chromosome (22.2%). The mosaicism rate was not significantly different between the Group II and III embryos (25.8% vs. 37.0%, p=0.28). The distribution of sex chromosomal aneuploidies was significantly different in Group III embryos (22.2% male vs. 55.5% female, p<0.0001). Conclusion: In conclusion, surplus poor-quality embryos rejected from clinical utilization at the cleavage stage may develop into viable blastocysts with normal chromosomal status for at least 5 chromosomes. Recovery of euploidy during poor-quality embryo transition from cleavage stage to blastocyst, could provide an alternative choice for ET.