Oocyte cryopreservation as an adjunct to the assisted reproductive technologies

To the Editor: Cryopreservation has been an integral tool in the development of modern assisted reproductive technologies, beginning with sperm cryopreservation in 1953 and extending to embryo cryopreservation in 1983, with the evolution of in-vitro fertilisation (IVF) and embryo transfer as a major tool in the treatment of infertility.1 Until recent times, however, there has been a lack of reliable cryopreservation methods for human oocytes. The world’s first recorded pregnancy arising from frozen oocytes occurred in Australia in 1984,2 and although occasional live births following oocyte cryopreservation were subsequently announced,3 it was another 11 years before more reliable protocols were developed4 — hundreds of live births have since been reported.5 The most common protocol follows that of embryo cryopreservation, using slow freezing with propanediol as the cryoprotectant, although rapid vitrification methods are also being developed.