Cryopreservation of Human Unfertilized and Fertilized Oocytes

Cryopreservation of human fertilized oocytes and embryos are nowadays well established in IVF practice with a wide range of clinical applications. However, freezing of unfertilized MII oocytes turned out to be one of the greatest challenges in the field of human reproductive cryobiology since the protocols remained ineffective for over 25 years. Only in the last 10 years the efficiency and safety of oocyte cryopreservation tremendously improved with the realization that zona hardening occurs in the process of cryopreservation and the introduction of vitrification. The possibility to cryopreserve unfertilized oocytes introduces new applications in the field of cryopreservation. We have now the opportunity to preserve fertility for cancer patients or to freeze oocytes for IVF patients when now sperm is available at the day of pick-up. This chapter will be dedicated to the vitrification of unfertilized MII oocytes and fertilized oocytes (pronuclear or zygote stage). An overview on the different indications for both stages of development will be described in the first part of this chapter. The second part will be about the technical and practical description of the vitrification process using hermetically closed and thus aseptic systems such as the Vitrisafe as carrier device. Finally, an overview on the clinical aspect, including our experience, will be given.