Assisted Hatching at the Time of Warming Improves Pregnancy and Implantation Outcomes for Vitrified Human Expanded Blastocyst Transfer

Vitrification has been focused on as a promising approach for human blastocyst cryopreservation, but few reports are available on the effect of assisted hatching (AH) in conjunction with human vitrified blastocyst transfers. Therefore, in this study, AH with acidic Tyrode was performed at the time of warming of vitrified blastocysts before transfer in order to improve the implantation and pregnancy rates. In the AH group, 13 clinical pregnancies (54.2%) and 15 implantations (36.6%) out of 41 blastocysts transferred were obtained. In the non-AH group, 1 clinical pregnancy (12.5%) and 1 implantation (6.7%) out of 15 blastocysts transferred were obtained. AH on the vitrified blastocysts after warming improved the implantation rate significantly (P<0.03). The pregnancy rate was also increased statistically in the AH group (P<0.05). The results suggest that the vitrification procedure may cause hardening of the zona pellucida and AH of vitrified blastocysts would be useful for clinical application.