Human Oocyte Cryopreservation - An Emerging ART Technique: Are We Heading in the Right Direction?

Abstract

Oocyte cryopreservation is a promising adjunct to human assisted reproductive technology. Slow rate freezing has been the cryopreservation standard for storage of sperm, embryos and, subsequently, oocytes. However, earlier concerns regarding damage to the meiotic spindle, loss of cortical granules and the low success rates as compared to the relative success of embryo cryopreservation caused little interest until the 1990s. Interest increased when many studies indicated that acceptable oocyte survival, in vitro fertilization, normal embryos and adequate blastocyst development can be achieved with oocyte cryopreservation. Recently introduced oocyte vitrification techniques are proving to be more efficient. Survival rates are close to 100% and developmental rates are similar to those achieved with fresh oocytes. This efficiency opens the way to the widespread application of the technique in various medical, legal, and social situations, even to replace embryo cryopreservation with the oocyte cryopreservation. Oocyte vitrification has dominated slow freezing to such an extent that it may soon become the exclusive cryopreservation choice, especially considering that potential disease transmission problems commonly associated with vitrification due to direct exposure of oocytes to liquid nitrogen can be eliminated by using the proper techniques and devices. Furthermore, cryopreservation of immature oocytes, ovarian follicles, ovarian tissue and whole ovary are other emerging technologies. Oocyte cryopreservation has tremendous opportunity for preserving fertility in cancer patients, for those who may not have sperm following oocyte retrieval and for those women who wish to delay their motherhood. The purpose of this article is to review the history of oocyte cryopreservation, its applications, current cryopreservation techniques and future trends for fertility cryopreservation, to determine if oocyte cryopreservation is proceeding in the right direction.