Cryopreservation of human prophase I oocytes collected from unstimulated follicles

Objective: To evaluate the cryopreservation of immature human oocytes obtained from unstimulated ovarian tissue. Design: Immature prophase I oocytes were obtained from unstimulated follicles and were either cryopreserved or cultured as controls. Cryopreservation was performed in a programmable freezing machine using one of two protocols. Method I (n = 133) used a one-step addition of cryoprotectant followed by a slow freeze and thaw protocol. With method II (n = 95), the cryoprotectant was added in a stepwise manner with cryopreservation performed in the presence of 0.2 M sucrose followed by rapid freezing and thawing. Setting: Basic research center at a medical school. Patients: Patients undergoing oophorectomy for nonovarian pathology. Main Outcome Measures: Rates of survival and maturation to metaphase II were compared between control oocytes and oocytes cryopreserved with methods I and II. Results: With method I, a survival rate of 15.6% was obtained with 58.3% of surviving oocytes reaching metaphase II after culture compared with 50.0% of nonfrozen control oocytes. Method II produced a survival rate of 43.3% with 27.3% maturing to metaphase II. Maturation of control oocytes for method II was 46.4%. Although the survival rate with method II was significantly higher than with method I, the rate of in vitro maturation to metaphase II showed no difference. Conclusions: These results demonstrate that human prophase I oocytes obtained from unstimulated antral follicles are capable of meiotic maturation after cryopreservation.