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

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. 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. University hospital-based fertility center. Stimulated patients undergoing IVF/ICSI treatment donated oocytes left over during their infertility treatment. 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. Survival rate, maturation rate and kinetics, and activation potential. 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. A pool of donated human oocytes could be established using slow controlled-rate freezing. Immature oocytes should be frozen after in vitro maturation.