Current status of the cryopreservation of human unfertilized oocytes.

Cryopreservation facilitates the long-term storage of oocytes from patients in danger of losing ovarian function and allows greater flexibility in fertility services for other patients. If some of the oocytes collected following ovulation stimulation are stored prior to fertilization, this alleviates many of the ethical concerns associated with embryo preservation. Concerns that cryopreservation could lead to disruption of the spindle and chromosomes, thus leading to genetic abnormalities of the offspring produced, mean that this procedure is not permitted in some countries. The recent spate of human live births from thawed oocytes has prompted the granting of the first licence allowing the use of thawed oocytes in the UK. However, the success rate of this procedure is still low and further research is required to refine these techniques and to develop new ones.