**5. Cryoinjury**

Oocytes and embryos are susceptible to different types of injuries following cryopreservation, which are collectively known as cryoinjuries. The extent of cryoinjuries to the frozen oocytes and embryos depends on many factors. The major factors are the type of CPA and freezing technique used for cryopreservation and the physiological quality, chilling sensitivity, plasma membrane permeability, tolerance for osmotic stress, developmental stage, and species of the oocytes and embryos [26, 31]. One of the primary focuses during the development of cryopreservation protocols is to minimize the possibilities of cryoinjuries to the preserved oocytes and embryos following freeze-thawing. The different types of cryoinjuries that oocyte and embryos are exposed to during the cryopreservation process are described below.
