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.