Delayed blastulation, multinucleation, and expansion grade are independently associated with live-birth rates in frozen blastocyst transfer cycles

Objective To identify blastocyst features independently predictive of successful pregnancy and live births with vitrified-warmed blastocysts. Design Retrospective study. Setting Academic hospital. Patient(s) Women undergoing a cycle with transfer of blastocysts vitrified using the Rapid-i closed carrier (n = 358). Intervention(s) None. Main Outcome Measure(s) Clinical pregnancy and live-birth rates analyzed using logistic regression analysis. Result(s) A total of 669 vitrified-warmed blastocysts were assessed. The survival rate was 95%. A mean of 1.7 ± 0.5 embryos were transferred. The clinical pregnancy, live-birth, and implantation rates were 55%, 46%, and 43%, respectively. The odds of clinical pregnancy (odds ratio [OR] 3.08; 95% confidence interval [CI], 1.88–5.12) and live birth (OR 2.93; 95% CI, 1.79–4.85) were three times higher with day-5 blastocysts versus slower-growing day-6 vitrified blastocysts, irrespective of patient age at cryopreservation. Blastocysts from multinucleated embryos were half as likely to result in a live birth (OR 0.46; 95% CI, 0.22–0.91). A four -fold increase in live birth was observed if an expanded blastocyst was available for transfer. The inner cell mass–trophectoderm score correlated to positive outcomes in the univariate analysis. The implantation rate was statistically significantly higher for day-5 versus day-6 vitrified blastocysts (50% vs. 29%, respectively). Conclusion(s) The blastocyst expansion grade after warming was predictive of successful outcomes independent of the inner cell mass or trophectoderm score. Delayed blastulation and multinucleation were independently associated with lower live-birth rates in frozen cycles. Implantation potential of the frozen blastocysts available should be included in the decision-making process regarding embryo number for transfer.