ABSTRACT
Although still considered to be an experimental procedure by many, oocyte cryopreservation is rapidly expanding, boosted by advances in cryopreservation methodologies. Especially in Italy, probably several thousands patients have been treated in the last few years by different slow cooling and vitrifi cation protocols. This imposes an urgent need to assess the clinical effi ciency of oocyte cryopreservation in comparison to other treatment strategies. The defi nition of clinical effi ciency in IVF has been a heatedly debated matter. In the United States, where costs of treatment are very high and not covered by national health agencies, the pregnancy rate per embryo transfer has been adopted as the most signifi cant parameter of effi ciency. Because it is clear that only a very small minority of oocytes (5-10%) has the potential to develop into a baby (1), in that country many clinics implement treatment strategies involving strict criteria of post-fertilization selection (e.g., blastocyst culture) and/or the simultaneous use of multiple embryos, to maximize the overall chances of at least one event of implantation per transfer. Such an approach can certainly give rise to comparatively high pregnancy rates, but also inevitably generates a high incidence of multiple pregnancies whose implications, in terms of prematurity, birth defects and healthcare costs, are increasingly considered unacceptable (see chap. 17). In Europe, especially in northern and Scandinavian countries, a different perception is emerging, according to which the rate of single healthy deliveries per cycle of stimulation is considered as the ultimate parameter to measure the clinical effi ciency of IVF treatments. This is currently leading to a decrease in the number of transferred embryos per transfer and to a more extensive use of the cryopreservation of “surplus” embryos. Fresh and frozen-thawed deliveries can be therefore taken into account together to express a comprehensive (cumulative) defi nition of clinical effi - ciency. From these and other considerations discussed in this chapter, it shows the cumulative pregnancy rate is probably the most correct approach to assess also the effi ciency of oocyte cryopreservation. Unfortunately, no large prospective controlled studies have been conducted so far with the aim of comparing the cumulative delivery rates of treatment cycles where embryo or oocyte cryopreservation (the latter in its various methodological versions) has been used. However, no matter how imperfect, current evidence suggests that the clinical effi ciency of oocyte cryopreservation is rapidly approaching the rates normally achieved by cryopreserved embryos. This is also indicated by a comparison of the rates of implantations elaborated on the number of oocytes used for a treatment cycle.
