Vitrification as an alternative means of cryopreserving ovarian tissue

Because of the simplicity of vitrification, many authors have investigated it as an alternative to slow freezing for cryopreserving ovarian tissue. In the last decade, numerous studies have evaluated vitrification of ovarian tissue from both humans and animals.Different vitrification solutions and protocols, mostly adapted from embryo and oocyte vitrification, have been applied. The results have been discrepant from species to species and even within the same species, but lately they appear to indicate that vitrification can achieve similar or even superior results to conventional freezing. Despite the encouraging results obtained with vitrification of ovarian tissue from humans and different animal species, it is necessary to understand how vitrification solutions and protocols can affect ovarian tissue, notably preantral follicles. In addition, it is important to bear in mind that the utilization of different approaches to assess tissue functionality and oocyte quality is essential in order to validate the promising results already obtained with vitrification procedures. This review summarizes the principles of vitrification, discusses the advantages of vitrification protocols for ovarian tissue cryopreservation and describes different studies conducted on the vitrification of ovarian tissue in humans and animal species.