Cryobanking of human ovarian tissue for anti-cancer treatment: comparison of vitrification and conventional freezing.

The first case of cryopreservation of human ovarian tissue with good survival of follicles after warming was described in 1996. Childbirth after cryopreservation of ovarian tissue is now a reality. Cryopreservation of ovarian tissue can be performed using one of two methods: conventional ("slow") freezing and cryopreservation by direct plunging into liquid nitrogen (so called vitrification or "rapid" freezing). Comparative investigations of vitrification and conventional freezing performed on mammalian ovarian tissue are limited, and authors present different conclusions. The higher effectiveness of vitrification in comparison with conventional freezing for human oocytes and embryos was shown, whereas data on human ovarian tissue are limited. The aim of different studies was to compare the safety and effectiveness of conventional freezing and vitrification of human ovarian tissue. Below we shortly summarize the results of some investigations with different conclusions. The discussion on the post-warming quality of follicles as well as on the problems of microbial contamination of cells in liquid nitrogen at vitrification is presented. In our opinion, for cryopreservation of human ovarian tissue, conventional freezing is more promising than vitrification.