ABSTRACT
The history of human oocyte cryopreservation is quite peculiar as compared to the development of other assisted reproduction technologies.
Since the fi rst successful case of human embryo cryopreservation 25 years ago, it has often been pointed out that freezing of excess embryos is only a temporary solution with many disadvantages and that it would often be more acceptable to store human oocytes to avoid ethical and legal problems. Indeed, shortly after the fi rst birth with frozen human embryos, a similar clinical success with frozen human oocytes was announced. However, the enthusiasm for the announcement of the fi rst pregnancies with frozen eggs was not followed by a rapid integration of the technique into the IVF clinical routine and, unlike the early and fast spread of embryo freezing, oocyte cryopreservation was and still is considered an experimental technique. Lessons learned from the general history of IVF show us that techniques indispensable to solving a problem have been rapidly adopted in the clinical routine before displaying evidence of safety. Embryo cryopreservation was developed inside the unavoidable dilemma of “freezing or wasting.” On the contrary, oocyte cryopreservation was an optional choice. Ethical concerns were not powerful enough to push clinical research and application in oocyte cryopreservation. This is the main reason why those early fully successful clinical applications remain anecdotal. The postulated intrinsic cryo-vulnerability of the mature oocyte raised safety concerns and became a major constraint. It was thanks to the basic biological studies of excellent researchers in reproductive cryobiology that many of those concerns were alleviated in the 1990s allowing the clinical resumption of oocyte cryopreservation by the end of the decade. A relatively intensive and, in some cases, routine application has been performed only in Italy, due to the recent restrictive legal regulation of IVF in that country. Variations in the results reported from different countries and IVF teams makes it still diffi cult to measure the true success of the procedure even though, in some reports, it seems to equal the embryo freezing effi ciency. In the past few years, the clinical application of egg storage has partially shifted to vitrifi cation, despite the absence of suffi cient basic biological studies addressing safety issues. Recently, the proposal of novel applications, such as the debated egg storage for non-medical indications to postpone maternity in young women, as well as the development of commercial interests, have prompted an acceleration in the spread of oocyte cryopreservation.
