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.