Day of blastulation correlates with ploidy status and serves as a useful non-invasive parameter for ranking embryos from non-PGT-A patients for transfer

BACKGROUND AND AIM Embryologists continue to strive to establish non-invasive parameters for ranking embryos to prioritize the ones with the highest chance of pregnancy success. Embryo morpho-kinetics have been correlated with implantation success. Previous studies have demonstrated that day 5 blastocysts result in higher implantation and pregnancy success as compared to day 6 blastocysts [1,2]. We aimed to test the hypothesis that embryos reaching an expanded blastocyst stage on day 5 are more likely to be euploid compared to their day 6 counterparts. METHODS We conducted a blinded retrospective review of patients undergoing PGT-A. Information from 253 women, aged 25 to 44, undergoing IVF/ICSI and PGT-A from January 1, 2022, to December 31, 2023, from which n = 1161 embryos were biopsied and PGT-A tested by Next Generation Sequencing (NGS) and compared. Chi-square analysis was conducted to determine differences between the groups with a p-value <0.05 considered statistically significant. RESULTS Of the 1161 biopsied and PGT-A tested embryos, 688 were day 5 blastocysts and 466 reached the blastocyst stage on day 6. The remaining 7 embryos were expanded blastocysts on day 7. The proportion of euploid embryos among day 5 blastocysts (49.4%) was significantly greater (p<0.0001) than that of day 6 blastocysts (32.8%) – Table 1. Corresponding aneuploidy rates were lower (p<0.0001) on day 5 (31.1%) compared to day 6 (45.3%). There was not any difference between High Level Mosaics (HLM); Low Level Mosaics (LLM) or no result reports observed (Figure 1). CONCLUSIONS Our results suggest that the genetic composition of an embryo is associated with the rate of embryo development, with day 5 blastocysts demonstrating a significantly higher likelihood of being euploid. This information is clinically important and provides valuable, non-invasive criteria regarding embryo quality, which can be used in embryo selection to improve clinical outcomes in non-PGT-A patients.