LAUSR

Objective Recent data demonstrate higher aneuploidy rates in day 7 embryos. It is unknown if increased aneuploidy rates are limited to specific embryos with slower development or if the presence of slower development indicates higher aneuploidy risk for a patient's entire embryo cohort. This study compares aneuploidy rates in women with some slow-developing embryos to those whose embryos blastulate only on days 5 and 6. Design Retrospective study Materials and Methods 21,237 embryos retrieved from 4,314 IVF cycles between January 2017 and March 2019 were evaluated. Embryos underwent blastocyst-stage preimplantation genetic testing via next-generation sequencing. Embryos were included from two groups. Group 1 was women whose IVF cycles yielded embryos with day 5 or 6 blastulation as well as delayed blastulation (day 7). Group 2 included women who only produced day 5 or 6 blastocysts. Euploidy rates for day 5 or 6 blastocysts were compared between groups. Within Group 1, euploidy rate of day 5 or 6 blastocysts was compared to euploidy rate of day 7 blastocysts. A generalized mixed effects model determined statistical significance, with p Results Group 1 consisted of patients who had some embryos blastulate on day 7. The group had 3,416 embryos undergoing blastulation on day 5 or 6 and 1,012 embryos undergoing blastulation on day 7. Group 2 consisted of 16,809 embryos from women whose developing blastocysts expanded prior to the end of day 6. Overall euploidy rate for day 5 or 6 blastocysts from Group 1 was 56.0% (binomial 95% CI 54.3%-57.7%). Day 5 or 6 blastocysts from Group 2 had an overall euploidy rate of 58.1% (binomial 95% CI 57.3%-58.8%). There was no statistically significant difference in euploidy rates for day 5 or 6 blastocysts between groups (p=0.79). Overall rate of euploidy for day 7 blastocysts from Group 1 was 40.6% (binomial 95% CI 37.6%-43.7%). Within Group 1, a significantly lower rate of euploidy was observed in day 7 blastocysts when compared to their day 5 or 6 blastocysts (p Conclusions Euploidy rates for day 5 or day 6 blastocysts were not impacted by the rate of development of other embryos within the same cohort. Each embryo's risk appears to be independent. These results indicate that patients who have some slow-developing embryos are not at increased risk of aneuploidy in their day 5 and day 6 embryos. Disclosures None Funding None