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Abstract Study question Does the implementation of one-step fast warming protocol affect the post warming quality of embryos and/or the reproductive outcome in frozen embryo replacement cycles? Summary answer The implementation of a one-step fast warming protocol provides similar survival, pregnancy, and clinical pregnancy rates with standard warming protocols. What is known already Cryopreservation process presents a significant challenge for embryos, as the formation of ice crystals can be lethal to their cells. Therefore, effective cryopreservation protocols are essential to mitigate this risk. Vitrification method protects the cells during cryopreservation by transforming water from a liquid state to a glass-like phase, thereby preventing the ice crystals formation. Moreover, the warming procedure can itself contribute to ice crystal formation, particularly through recrystallization. Studies have shown that embryo survival is related to warming rate and a one-step fasting warming protocol can be equally or more effective than the conventional protocol. Study design, size, duration This prospective randomized study was performed at Embryolab Fertility Clinic, in Thessaloniki, Greece between July and December 2023 and included 118 frozen embryo transfers. Both study and control group included only expanded blastocysts of good quality (AA or AB according to Gardner’s criteria). Control group was matched to the study group according to treatment, time period, woman age, quality of embryos and number of transferred embryos. The embryos were vitrified using open system. Participants/materials, setting, methods Fast warming group included embryos that were warmed using the one-step warming protocol: the embryos were exposed to 1M sucrose solution for 1’ at 37 °C and then immediately placed into culture media where laser-assisted hatching was performed. Control group included embryos that were warmed using conventional protocol: 1’ in 1M, 2’ in 0.5M, 2’ in 0.25M and 3’ in washing solution at room temperature and then placed into culture media for laser-assisted hatching. Main results and the role of chance The analyzed cases were 118 in total, 59 in the fast-warming group and 59 in the control group. Survival rate was 100% in both groups. Pregnancy rate (positive b-HCG) was not significantly different between the two groups: 72.41% in the fast-warming group and 67.79% in the control group (p = 0.687). Clinical pregnancy rate was also not significant between the two groups: 78.26% in the fast-warming group and 81.81% in the control group (p = 0.753). Limitations, reasons for caution The study included a limited number of cases, and information on the live birth rate was still pending. To establish the efficacy of fast warming conclusively, it is recommended that additional prospective randomized studies be conducted to validate its potential benefits. Wider implications of the findings One-step fast warming protocol resulted in similar survival rates post warm compared to the conventional warming protocol, while pregnancy and clinical pregnancy rates were not significantly different. Furthermore, it is worth noting that by minimizing the duration of the warming protocol, the workflow efficiency in the IVF laboratory is enhanced. Trial registration number N/A
Karagianni et al. (Mon,) studied this question.
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