Fertility preservation with immature and in vitro matured oocytes.

The development of an effective oocyte-freezing program will have a major impact on clinical practice in reproductive medicine and will serve as a powerful tool to preserve fertility for teenage girls and young women without male partners or for those individuals who are affected by malignancies. It will also be beneficial to infertile couples who have moral or religious objections about embryo cryopreservation. In addition, a successful oocyte cryopreservation program will eliminate the need for donor and recipient menstrual cycle synchronization and will enable the establishment of oocyte banks, which would facilitate the logistics of coordinating egg donors with recipients. Recent advances in vitrification technology have markedly improved the oocyte survival rate after thawing, and the pregnancy rate is comparable with that achieved with fresh oocytes. However, most studies were performed using in vivo matured oocytes for vitrification. The objective of this article was to review whether immature and in vitro matured human oocytes can be vitrified successfully. The results indicated that although healthy live births can be achieved from the combination of in vitro maturation (IVM) oocytes and vitrification, vitrification of in vitro matured oocytes is less effective than vitrification of in vivo matured oocytes. The results suggest that oocytes should be vitrified at the mature metaphase II stage following IVM rather than at the immature germinal vesicle (GV) stage because the potential of oocyte maturation is reduced by the vitrification of immature oocytes at the GV stage. Thieme Medical Publishers.