Oocyte cryopreservation

Cryopreservation of human oocytes has been employed with little success in clinical practice, even though it may solve the legal and ethical problems linked to embryo freezing. Various attempts to cryopreserve human oocytes h ale mostly been unsuccessful, leading to low oocyte survival rates after th awing, and the search for an optimal protocol for oocyte cryopreservation r emains elusive. A preliminary study was undertaken to evaluate some of the factors influencing the survival rate of human oocytes and the efficiency o f intracytoplasmic sperm injection (ICSI) as an insemination procedure, A t otal of 38 women with tubal infertility were enrolled in the study. The cry opreservation procedure consisted of a slow freeze-rapid thawing technique using 1,2 propanediol and sucrose as cryoprotectants. The overall oocyte su rvival rate was similar to 60%. A better survival rate was obtained when th e oocytes were cryopreserved in the presence of partially removed cumulus o ophorus rather than in the presence of totally enzymatically removed cumulu s oophorus. The cryoprotectant concentration and the equilibration time als o appear to influence the oocyte survival rate. ICSI may be an efficient me thod of achieving a satisfactory outcome in terms of fertilization in cryop reserved human oocytes. Embryonic morphological duality does not seem to be compromised by cryopreservation. In conclusion, these data show that cryop reservation may ensure that the integrity of the human oocyte is adequate f or normal fertilization and embryo development.