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.

Reliable oocyte cryopreservation protocols are important for patients for whom embryo cryopreservation is unacceptable under some national laws or religions, and in whom there may be sperm collection problems or unexplained azoospermia during IVF procedures.

We report four live births, one ongoing pregnancy, and an ectopic pregnancy following oocyte cryopreservation. Three of these cases involved religious opposition to embryo freezing. In each case, only two oocytes were fertilised fresh and the remainder frozen. No pregnancies resulted from the fresh embryo transfers, and the frozen oocytes were subsequently thawed, fertilised, and transferred, to produce the pregnancies. Two cases involved idiopathic azoospermia on the day of IVF, while in another, no sperm could be obtained from testicular aspiration on the day. Oocytes from these men’s partners were frozen until the sperm supply problems were resolved.

As these cases demonstrate, oocyte cryopreservation can serve as a valuable adjunct to assisted reproduction programs, by providing a solution to the occasional logistical problems caused by unavailable spermatozoa. It also provides another option for patients with ethical or religious objections to the cryopreservation of embryos, and for fertility preservation in women with cancer facing chemotherapy or for women who may wish to insure against age-related fertility decline.

The six pregnancies described here arose from embryo transfers in 13 women who had oocytes cryopreserved. The results, combined with others achieved worldwide, suggest that oocyte cryopreservation may at last be coming of age.