Blastocyst development rate impacts outcome in cryopreserved blastocyst transfer cycles

Objective: To assess cycle outcome among day 5 and day 6 cryopreserved frozen-thawed blastocyst embryo transfers (FBET). Design: Retrospective cohort study. Setting: Military-based assisted reproduction technology (ART) center. Patient(s): One hundred seventy-two nondonor, programmed cryopreserved embryo cycles. Intervention(s): Fully expanded blastocysts on day 5 were cryopreserved on day 5, and those achieving this state on day 6 were cryopreserved on day 6. Leuprolide acetate was given for ovulation inhibition, and endometrial supplementation was by oral and vaginal estradiol. Progesterone in oil was administered, and blastocyst transfer occurred in the morning of the sixth day of progesterone. Main Outcome Measure(s): Implantation, pregnancy, and live-birth rates. Result(s): Fresh and frozen cycle characteristics were similar between groups. Day-5 FBET had statistically significantly higher implantation rates (32.2% vs. 19.2%), which remained significant even when adjusting for covariates (odds ratio: 1.91; 95% confidence interval, 1.00, 3.67). Live-birth rates trended toward improvement after adjusting for covariates (odds ratio: 1.18; 95% confidence interval, 0.61, 2.30). Conclusion(s): Cryopreserved day-5 blastocysts have higher implantation rates and trend toward improved pregnancy outcomes compared with cryopreserved day-6 blastocysts. This suggests that embryo development rate may, in part, predict implantation and subsequent FBET outcomes, although embryos not achieving the blastocyst stage until day 6 still demonstrate acceptable outcomes.