Research question: Do embryos warmed using a one-step rehydration protocol with a more efficient workflow result in comparable pregnancy rates to the standard multi-step rehydration protocol?
Design: A retrospective cohort study of 3439 frozen embryo transfers (FET). Clinical outcomes of 833 FETs using a one-step rehydration protocol were reviewed and compared with results from the control group (2606 FETs using standard multi-step rehydration protocol). Primary outcome was ongoing pregnancy rate. Secondary outcomes were survival, positive pregnancy, clinical pregnancy, implantation and miscarriage rates.
Results: Survival rates were identical between the two groups (99.5%). Clinical pregnancy rate was 63.0% in the one-step warming protocol, comparable to 59.9% in the multi-step rehydration protocol. A significant increase was observed in the ongoing pregnancy rate with 60.4% in the one-step rehydration versus 55.4% in the multi-step rehydration group (P = 0.011); implantation rate was 63.6% versus 57.0% (P = 0.0005). The miscarriage rate of 4.0% in the one-step rehydration protocol was significantly lower compared with 7.6% in the multi-step rehydration protocol (P = 0.0001). Comparable outcomes persisted even when the analysis was extended to embryos that had and had not undergone preimplantation genetic testing (PGT), as well as day of development of the blastocysts. When controlling for variables of age, PGT, blastocyst development day and embryo expansion, rapid warming significantly increased chances of an ongoing pregnancy (adjusted OR 1.264, 95% CI 1.076 to 1.484).
Conclusion: A one-step rehydration protocol resulted in identical survival rates and improved ongoing pregnancy rates compared with the multi-step rehydration technique.
Keywords: Blastocysts; One-step rehydration protocol; Pregnancy rate; Vitrification; Warming.
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