Should we should consider day 3 blastomere number during single vitrified-warmed blastocyst transfer cycle? A retrospective study

The present study investigated whether day 3 blastomere number has an effect on the clinical outcomes during single vitrified-warmed blastocyst transfer cycles. A total of 3294 vitrified-warmed single day 5 blastocyst transferred cycles were analyzed in this retrospective study from January 2018 to December 2021. The cycles were divided into >= 7 and < 7 blastomere groups depending on the day 3 embryo blastomere number. The clinical outcomes were compared between the two groups, moreover multivariate logistic regression analysis was conducted to investigate the correlation between the number of day 3 blastomeres and clinical outcomes. The chi-square test demonstrated that the rates of clinical pregnancy and live birth were significantly higher in the >= 7 blastomere group compared to the < 7 blastomere group with respect to single high-quality blastocyst transfer cycles. Conversely, these rates were similar in the two groups with respect to single low-quality blastocyst transfer cycles. These results were confirmed by multivariate logistic regression analysis. However, the miscarriage rate was higher in the < 7 blastomere group than in >= 7 group during low-quality blastocyst transfer cycles. These results suggested that day 3 blastomere number should be considered during single vitrified-warmed blastocyst transfer cycles. Thus, blastocsyts derived from >= 7 blastomere embryos are preferred when choosing the same quality blastocysts.