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Research Question: Can immature oocytes vitrified and warmed using a short protocol survive and resume meiosis?, Design: This study examined modifications of oocyte vitrification and warming protocols that reduce the length of exposure to vitrification and warming solutions. In total, 561 germinal vesicles and 218 metaphase I oocytes that were immature at oocyte retrieval were vitrified at room temperature for 2 min. Warming was performed at 37°C for 2 min. Resumption of meiotic activity was evaluated after 24 and 48 h of culture. Two different commercially available vitrification and warming kits were used for comparison., Results: Ninety-five percent of germinal vesicles survived, with no difference observed between the kits. The survival of metaphase I oocytes was, on average, 95.4% and did not differ significantly between the kits. Of the 533 germinal vesicles that survived, 491 converted to metaphase I oocytes (92.1%). After culture for 48 h, 54.4% converted to metaphase II oocytes. In addition, of the 208 metaphase I oocytes that survived warming, 84.1% converted to metaphase II oocytes after 24 h of culture. These maturation rates were similar to those of non-vitrified oocytes., Conclusions: Vitrification and warming of oocytes at different nuclear maturation stages can be performed with 2 min of exposure to hypertonic solution and 2 min of exposure to hypotonic solution, respectively. This approach reduces exposure of the oocytes to room temperature during dehydration and rehydration. Warming in 0.5M sucrose helps to maintain and support the potential of oocytes to resume nuclear meiotic activity, and conversion from germinal vesicles to metaphase I and metaphase II oocytes., (Copyright © 2024 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.)

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., (Copyright © 2023 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.)

Blastocyst culture has reduced the number of embryos transferred per cycle, whilst simultaneously creating new quandaries regarding supernumerary blastocyst cryopreservation. This retrospective study was undertaken to compare a slow freezing protocol to a vitrification protocol for cryopreservation of day 5 and day 6 human blastocysts. To demonstrate this, the survival, implantation rate and pregnancy rates were compared after thawing, assessment and embryo transfer of 86 consecutive day 5 and day 6 thawed blastocyst transfer cycles from January 1, 2002 to December 31, 2003. Seventy-one day 5 slow-frozen (SF) blastocysts were thawed and 59 embryos survived the thawing (83.1%). An average of 2.5 SF blastocysts was replaced per embryo transfer, resulting in a pregnancy rate of 16.7% (4/24). Concurrently, 41 vitrified (VIT) blastocysts were thawed and all 41 survived the thawing process (100%). An average of 2.0 VIT blastocysts was replaced per embryo transfer, resulting in a pregnancy rate of 50% (10/20). Survival, pregnancy and implantation rates of day 5 VIT blastocysts have significantly increased (P < 0.01, P < 0.02 and P < 0.01 respectively) over day 5 SF blastocysts. A similar trend was observed with day 6 blastocysts.