Section 4 - Cryopreservation of oocytes

Summary

An effective oocyte cryopreservation program benefits infertile couples with moral or religious objections about cryopreservation of embryos. When considering all pregnancies and live births obtained from cryopreserved oocytes using the classic slow-freezing method, the survival rates averaged approximately 50%. The percentage of live births per thawed egg ranges from 1 to 10% using the classic slow-freezing protocols. Recently, improved survival and pregnancy rates have been reported using modified slow-freezing procedures, particularly increased sucrose concentration in the suspending solution, and the use of sodium-free freezing solutions. Several attempts have been made with immature human oocytes. Although survival rates seemed to be improved by the slow-freezing method, poor in vitro maturation (IVM) and fertilization are major problems associated with immature egg freezing. Rapid cooling (vitrification) of human oocytes has resulted in relatively higher survival rates. This study suggested that better results can be achieved by vitrifying mature oocytes rather than immature oocytes.