Slow controlled-rate freezing of human in vitro matured oocytes: effects on maturation rate and kinetics and parthenogenetic activation

Objective: To create a pool of frozen donated human oocytes and find the optimal stage for slow controlled-rate freezing of human in vitro matured oocytes. Design: Oocytes at different developmental stages of maturation (germinal vesicle, metaphase I, or metaphase II) and oocytes that failed to fertilize after IVF or intracytoplasmic sperm injection (ICSI) were frozen using a slow controlled-rate freezing protocol. Frozen/thawed oocytes were artificially activated to verify activation potential and compared with oocytes that were not frozen. Setting: University hospital-based fertility center. Patient(s): Stimulated patients undergoing IVF/ICSI treatment donated oocytes left over during their infertility treatment. Intervention(s): Human oocytes were frozen at different stages of maturation. Fresh and frozen/thawed oocytes were activated by electrical pulses followed by incubation in 6-dimethylaminopurine. Main Outcome Measure(s): Survival rate, maturation rate and kinetics, and activation potential. Result(s): Human oocytes at all developmental stages have high survival rates after slow controlled-rate freezing. Frozen/thawed germinal vesicle oocytes showed decreased and delayed maturation after thawing. Activation potential was not affected. Conclusion(s): A pool of donated human oocytes could be established using slow controlled-rate freezing. Immature oocytes should be frozen after in vitro maturation. (Fertil Steril (R) 2011;96:624-8. (C)2011 by American Society for Reproductive Medicine.)