Cryopreservation of female fertility

Preservation of female fertility is an important issue today. There are a few effective clinical options for preserving female fertility. Conventional IVF followed by embryo cryopreservation is the only established procedure but is not applicable to all women. Oocyte cryopreservation avoids the ethical and moral concerns related to cryopreservation of embryos but conventional slow freezing methods are associated with low survival rate of oocytes. The main objective of this translational research thesis was to develop an efficient and safe methodology for oocyte cryopreservation that is clinically applicable for female fertility preservation. Specific research objectives were to investigate cryobiology of oocytes in terms of: (1) cryoprotectant (CPA) toxicity effect on oocyte ultra-structures and embryonic developmental potential; (2) Vitrification versus conventional slow freezing of oocytes and their effects of oocyte structures and embryonic developmental potential; (3) Vitrification of embryos using the McGill Cryoleaf and its effect of embryonic development and DNA fragmentation; (4) Clinical efficacy of oocyte vitrification in prospective clinical trials; (5) Effects of oocyte vitrification in terms of the clinical obstetrical and perinatal outcomes; (6) Clinical applications of vitrification of oocytes for preservation of female fertility. The CPA mixture of ethylene glycol (EG) and 1,2-propanediol (PROH) was found to be the most suitable combination for oocyte vitrification, resulting in high embryo development and the least DNA fragmentation. Vitrification of oocyte using the CPA mixture of EG and PROH in combination with the McGill Cryoleaf system is superior to the conventional slow-cooling method, resulting in better preservation of egg ultra-structures and functions. The reduced embryonic development potential of cryopreserved oocyte is related to increased DNA fragmentation and activation of caspase enzymes. Vitrification of human oocytes using the McGill Cryoleaf system results in a clinical pregnancy rate that is comparable to the mean IVF clinical pregnancy rates in Canada, United States, and Europe. This novel oocyte vitrification system is associated with normal obstetrical and neonatal outcomes and healthy newborns. Vitrification of oocytes can be used safely for human reproductive medicine. In conclusion, oocyte vitrification using the McGill Cryoleaf system is efficient, safe, and innovative. This novel oocyte vitrification strategy can be introduced for clinical use in the preservation of a woman’s fertility.