Outcomes of Vitrified Early Cleavage-stage and Blastocyst-stage Embryos in a Cryopreservation Program: Evaluation of 3,150 Warming Cycles

Objective: To assess the outcomes achieved after Cryotop vitrification of both early cleavage and blastocyst-stage embryos and to determine whether the embryo developmental stage and embryo quality as well as the origin of the embryos (ovum donation cycles, patients' own oocytes) and the endometrial preparation for the embryo transfer had any effect on the final outcome.

Design: Observational study.

Setting: Private university-affiliated IVF center.

Patient(s): Women undergoing 3,150 warming cycles whose embryos were vitrified due to various reasons.

Intervention(s): Vitrification by the Cryotop open device.

Main Outcome Measure(s): Delivery rate (DR) per warming cycle.

Result(s): Survival rate was 95% (5,722 out of 6,019 embryos). The percentage of intact embryos at warming showing 100% blastomere survival was 93% (95% CI 90.1%-95.3%) for day 2 and 95% (95% CI 94.3%-95.7%) for day 3; 3,057 embryo transfers were performed (3% cancellation rate). The DR/warming cycle was 32.5% (95% CI 30.9%-34.2%). Slight differences in survival rate were found [94.9% (95% CI 93.0%-96.8%) for day 2, 94.2% (95% CI 93.4%-94.9%) for day 3, 95.7% (95% CI 94.5%-96.9%) for day 5, and 97.6% (95% CI 96.9%-98.6%) for day 6]. Overall implantation, clinical pregnancy, ongoing pregnancy, and live birth rates per warming cycle were 35.5% (95% CI 33.5%-38.5%), 41.7% (95% CI 39.9%-43.4%), 32.6% (95% CI 31.0%-34.2%), and 38.1% (95% CI 36.4%-39.8%) respectively. The linear regression model considering embryo developmental stage, ovum donation or patient's own oocytes, and hormonal replacement therapy or natural cycle for endometrial preparation (odds ratio 1.179; 95% CI 0.912-1.277) showed no impact on the DR.

Conclusion(s): Highly successful cryopreservation of all embryo developmental stages is possible with the use of the Cryotop system. There are no variables clearly exerting a negative effect on the survival and delivery rates.