Observational clinical follow-up of oocyte cryopreservation using a slow-freezing method with 1,2-propanediol plus sucrose followed by ICSI.

Background: The value of oocyte cryopreservation remains controversial. Two major problems exist: poor survival and injury to the oocyte meiotic spindle after freezing and thawing.

Methods: For slow oocyte cryopreservation, we used 1.5 mol/l 1,2-propanediol and 0.3 mol/l sucrose. We waited 3 h after thawing for possible recovery of the meiotic spindles before performing ICSI.

Results: Forty-three women undergoing IVF or ICSI cycles cryopreserved some or all of their harvested oocytes; of these, 20 thawed their cryopreserved oocytes for personal use and one for donation. The survival rate of oocytes after thawing was 75%, with 67% of oocytes fertilizing normally after ICSI. All 21 cycles (100%) resulted in fertilization and embryo transfers. Seven pregnancies (33%) resulted. Four women delivered five babies with normal karyotypes. Three conceptions are ongoing. Compared to 38 cycles of frozen-thawed embryos at the pronuclear stage in the same period, the percentages of survival, pregnancy and implantation were similar. Additionally, four unmarried women with white blood cell diseases underwent oocyte freezing before preconditioning treatment for haematopoietic stem cell transplantation.

Conclusions: This protocol achieved reproducible success of survival, fertilization and pregnancy for freezing and thawing of human oocytes. The 3 h post-thaw incubation could permit restoration of the meiotic spindles, thus facilitating normal fertilization.