Effects of duration of cryo-storage of mouse oocytes on cryo-survival, fertilization and embryonic development following vitrification

Purpose To investigate the effects of cryo-storage duration in liquid nitrogen on oocyte cryo-survival, fertilization and embryonic development following vitrification and warming. Methods Mature mouse oocytes were vitrified with McGill Cryoleaf and stored in liquid nitrogen for a period of 8–10 days, 90–92 days and 180–182 days, respectively. After warming, the survived oocytes were inseminated by intracytoplasmic sperm injection (ICSI) and cultured for 120 h. The rates of oocyte cryo-survival, cleavage and embryonic development were compared. Result(s) The oocyte cryo-survival rate declined following cryo-storage duration for 180–182 days (90.4 ± 7.9%) compared to that of the other two groups (97.4 ± 3.0% and 98.0 ± 3.3%). The fertilization rate in the group of 180–182 days (66.6 ± 22.0%) was also significantly reduced ( P < 0.05) compared with the groups of 8–10 days (92.2 ± 10.8%) and 90–92 days (94.7 ± 9.1%). In addition, the number of embryos developed to the blastocyst stage declined significantly ( P < 0.05) following long cryo-storage duration (72.1 ± 8.2%, 25.2 ± 3.8% and 5.5 ± 13.6%, respectively). Conclusion(s) The cryo-survival, fertilization rate and embryonic development of mouse oocytes are affected significantly, in an adverse manner, by the cryo-storage duration in liquid nitrogen.