ABSTRACT
Storage of unfertilized mammalian oocytes has numerous applications in both human and animal reproductive technologies. Cryopreserved human oocytes can assist in the treatment of human infertility, for example, where loss of fertility may be predicted following ablative anticancer treatments or in patients suffering premature ovarian failure; banking of excess oocytes produced as a result of in vitro fertilization (IVF) treatments; and donation of oocytes to others (storage giving the added advantage of allowing time to screen donors for disease). Oocyte cryopreservation could also serve as a means of delaying child bearing to an age when natural fertility and/or oocyte quality has declined. Applications in animal management include, amongst the domestic species, preservation and cross-nation transport of economicallyimportant strains; the potential to restock depleted herds following outbreaks of diseases such as foot and mouth; preservation of genetically modifi ed strains, thereby reducing the cost of continuous breeding and avoiding problems of genetic drift; and the preservation and management of endangered species. From an ethical and legal standpoint in clinical practice, many people view oocyte cryopreservation as preferable to embryo storage because concerns about parental ownership or consent for use are lessened with unfertilized gametes. In some countries, cryopreservation of human embryos is currently prohibited or strictly limited because of these considerations. In animal management, oocyte cryopreservation gives greater fl exibility in breeding programs than does embryo cryopreservation. Cryopreservation of mature oocytes is a relatively young science with a history of only 30 years. The fi rst live births from cryopreserved ovulated mammalian oocytes were reported by Whittingham in 1977 in mice (1) and subsequently by reports in a number of other species including rabbits (2), cows (3), horses (4), and over the past 20 years in humans (5-7). However, in most species success rates for cryopreserved oocytes have remained markedly poorer when compared with the cryopreserved embryos.
