Reassessing the conventional fertilization check: leveraging preimplantation genetic testing for aneuploidy to increase the number of transferrable embryos

RESEARCH QUESTION: Are some non-2PN zygotes normally fertilized, euploid and thus available for transfer? DESIGN: Retrospective cohort study of patient data from 1214 PGT-A cycles from a single private IVF clinic. A total of 152 non-2PN embryos were assessed by PGT-A with parent of origin assessment, and were compared with 4822 2PN embryos assessed by PGT-A. Transfer outcomes of euploid embryos were then compared. RESULTS: Over 40% of the tested non-2PN embryos were euploid. The 152 non-2PN (89 ICSI, 63 IVF), embryos were 2×0PN, 50×1PN, 24×2.1PN, 65×3PN, 9×4PN and 2×5PN. Of 4822 2PN embryos, 4737 (98.2%) were diploid, 1.4% polyploid and 0.4% haploid. Embryos resulting from 1PN zygotes were more likely to be haploid, and embryos resulting from 3PN and 4PN zygotes were more likely to be polyploid (P < 0.001). A total of 44 out of 89 (50%) ICSI embryos were either haploid or polyploid, significantly higher than those derived from IVF (16/63 [25.4%], P = 0.004). Maternal origin of polyploidy was more common in ICSI cases (P = 0.005). A total of 42% of the 93 diploid non-2PN embryos were also euploid, with diploid blastocysts from non-2PN zygotes likely to be euploid as those from diploid 2PN zygotes (P = 0.10). Twelve euploid 1PN, 2.1PN and 3PN embryos were transferred; two ongoing pregnancies and four live births have been reported. CONCLUSIONS: This approach extends the use of PGT-A in identifying more embryos available for transfer, has the potential to increase cumulative pregnancy rates and questions the value of the fertilization check.