Cryopreservation of human oocytes.

Cryopreservation is a well established technique by which preimplantation stage embryos can be stored for later use. However, it would be preferable to cryopreserve unfertilized oocytes to overcome the problems related to the ethical and legal status of the embryo. This procedure has been successful in mice, but attempts to extend this approach to other species have been less successful. In human in vitro fertilization (IVF) in particular, very few live births have been reported after the cryopreservation of oocytes. The reason for this lack of success is unclear. The widespread contention that compromised oocyte viability originates principally from damage to the meiotic spindle induced by cryopreservation conditions is unproven. The treatment of large groups of women has shown that pregnancies derived from stored oocytes can be achieved in a reproducible fashion, although success rates are still lower than those derived from frozen embryos. To date, human oocytes have been stored largely by applying methods originally designed for cleaving embryos. Therefore, it is reasonable to envisage that appropriate modification of current freezing techniques will increase survival rates and make oocyte storage an important option in IVF treatment.