Human oocyte ultravitrification with a low concentration of cryoprotectants by ultrafast cooling: a new protocol

Objective To evaluate the efficacy of a new ultravitrification technique with a low concentration of cryoprotectants. Design Ultravitrification research. Setting Private assisted reproduction center. Patient(s) Oocytes donated voluntarily with the aim of research. Intervention(s) Ultravitrification with different protocols of 100 mature oocytes and 100 immature oocytes divided in four groups to determine which is the adequate cryoprotectant concentration and the appropriate cooling solution. Main Outcome Measure(s) Human oocytes survival rate with low concentration of cryoprotectants by ultravitrification technique. Result(s) We obtained higher survival rates with slush nitrogen than with liquid nitrogen (92% vs. 56%) and better results with 2 M of cryoprotectants than with 1.5 M (92% vs. 60%). The best protocol was 2 M PrOH + 0.5 M sucrose + slush nitrogen with a mature oocytes survival rate of 92% (23 of 25) and immature of 88% (22 of 25). Conclusion(s) This ultravitrification technique is a new option to preserve human oocytes that avoids the use of a high cryoprotectant concentration while obtaining a high survival rate with a concentration of cryoprotectants typical of slow freezing.