Egg Freezing
Introduction:
The last few years have seen a significant resurgence of interest in human egg freezing due to numerous potential benefits. These benefits include: (1) The formation of donor "egg banks" to facilitate and lessen the cost of egg donation in women who are unable to produce their own viable eggs. This could eliminate the current practice of using fresh eggs which carries some risks of transmitting infectious diseases. (2) The provision of egg cryostorage for women wishing to delay their reproductive choices. (3) The freezing of eggs for female cancer patients about to undergo chemotherapy or other treatments that may be harmful to reproductive tissue.
Traditional cryopreservation protocols (i.e., those that have been used to successfully cryopreserve preimplantation embryos), have led to only a small percentage of live births due to a higher potential of chromosomal abnormalities in the resulting embryos from these oocytes. Further research is required to refine existing oocyte cryopreservation techniques and to develop new ones. We will investigate a new method for improving the cryopreservation (freezing) and thaw survival of human eggs.
Background
Human oocyte (egg) cryopreservation (freezing) has many potential advantages including formation of "egg banks" for those unable to produce their own oocytes, those wishing to delay childbearing or those about to undergo chemotherapy or other treatments that may be harmful to their reproductive function. Current slow freezing methods, with only slight modifications, are based on the procedure first described by Willadsen (1977) for the freezing of ovine and bovine embryos. The equilibration time and amount of permeating cryoprotective additive (CPA) as well as the concentration of sucrose are among most common changes between various protocols (Fabbri et al., 2001). Recent alterations include the use of low or sodium free freezing solutions (Azambuja et al., 2002; Quintans et al., 2002; Boldt et al., 2003). However, the basic principle, as outlined above, remains the same. Oocytes suspended in a solution containing CPAs are cooled and seeded to induce ice formation, dehydrated as the solution is cooled slowly at 0.3 o C/min to -30 o C or below, and plunged into Liquid Nitrogen (LN2) for storage. Routine egg freezing remains an elusive technique due to the fact that its success depends on multiple cryobiological factors (mechanical, chemical and thermal) that could influence the developmental potential of the oocytes. Furthermore, the human egg is the largest cell in the human body and its large content of water makes it susceptible to damage from freezing. Much of the recent research and clinical application has focused on traditional cryopreservation protocols (i.e., those that have been used to successfully cryopreserve preimplantation embryos), and these have led to only a small percentage of live births. Additionally, various research studies have shown that using traditional techniques to cryopreserve oocytes may cause disruption of the spindle and chromosomes and thus lead to a higher potential of chromosomal abnormalities in the resulting embryos that arise from these oocytes. We will investigate a new method for improving the cryopreservation (freezing) and thaw survival of human eggs.