Fast and furious: pregnancy outcome with one-step rehydration in the warming protocol for human blastocysts

Research Question The purpose of this study was to determine if embryos warmed using a one-step rehydration protocol with a more efficient workflow resulted in comparable pregnancy rates to the standard multi-step rehydration protocol. Design This was a retrospective cohort study of a total of 3439 frozen embryo transfers (FET). The study data includes a retrospective review of clinical outcomes of 833 FETs using a one-step rehydration protocol. This data set was then compared to results from the control group obtained from 2606 FETs where the standard multi-step rehydration protocol was used. The primary outcome was the ongoing pregnancy rate. The secondary outcomes were survival, positive pregnancy, clinical pregnancy, implantation, and miscarriage rates. Results Survival rates were identical between the two groups (99.5%). The clinical pregnancy rate was 63.0% in the one-step warming protocol, which was comparable to 59.9% in the multi-step rehydration protocol. However, there was a significant increase in the ongoing pregnancy rate with 60.4% in the one-step rehydration vs 55.4% in the multi-step rehydration group (p=0.011) as well as the implantation rate with 63.6% vs 57.0% (p=0.0005). Moreover, the miscarriage rate of 4.0% in the one-step rehydration protocol was significantly lower compared to 7.6% in the multi-step rehydration protocol (p=0.0001). These findings persisted even when the analysis was extended to PGT tested and untested embryos as well as day of development of the blastocysts. Conclusion These findings highlight that a one-step rehydration protocol resulted in identical survival rates and improved ongoing pregnancy rates compared with the multi-step rehydration technique.