P-503 Euploidy rate of day 4 fully developed blastocysts

Abstract

Abstract Study question Do embryos that fully developed to blastocyst at day 4 have high aneuploidy rates as assessed by preimplantation genetic analysis? Summary answer Fully developed blastocysts at day 4 had a high euploidy rate. What is known already In ART, it is considered important to use good quality blastocysts to increase the pregnancy rate after embryo transfer. Some reports have demonstrated a high pregnancy rate for embryos that fully developed to blastocysts on day 4 after IVF (Ozgur et al., 2021). Furthermore, it has been reported that the speed of embryo development is related to the rate of chromosome aneuploidy (Taylor et al., 2014). There are though, limited reports on the euploidy rate of embryos developed to blastocysts at day 4. Study design, size, duration This retrospective study analyzed 763 embryos (from 184 PGT-A cases) that underwent TE biopsy on day 5 between January to December 2022 to determine their ploidy status. Participants/materials, setting, methods Embryos cultured in a time-lapse incubator were divided into two groups: those that developed to blastocyst (Gardner’s classification: ≥ expansion grade 3) at day 4 (96-100 h) (D4(+) group) and those that did not develop to full blastocyst at day 4 (D4(-) group) and the euploidy rates were compared. Statistical analysis was performed using Fisher’s exact test to determine significant differences (P < 0.05). Main results and the role of chance The euploidy rate of the D4(+) group was 36.5% (80/219), which was significantly higher than the D4(-) group, 23.3% (127/544) (p < 0.01). Moreover, when considering the age of the female, for age ≤39 years, the rates were significantly higher in the D4(+) group (52.1% (61/117) and 35.4% (97/274) p < 0.01 respectively ). For age 40≥ years, it tended to be higher but was not significantly different in the D4(+) group vs D4(-) group (18.6% 19/102 and 11.1% 30/270 respectively). Even when limited to embryos that were graded as good quality blastocysts at day 5, the D4(+) group was significantly higher (p < 0.01) than the D4(-) group (55.0% (60/109) vs 36.1% (90/249)). Limitations, reasons for caution This was a retrospective study limited to day 5 embryos with biopsies taken after vitrification-warming. Wider implications of the findings These results demonstrate that embryos that had already developed to blastocyst at day 4 had a higher rate of euploidy compared to day 5 blastocysts. Thus, when performing PGT-A, biopsy of embryos that have already developed to blastocyst at day 4 are expected to be prioritised for transfer. Trial registration number not applicable