Vitrification of Human Immature Oocytes in IVM Program
The cryopreservation of immature GV oocytes by vitrification is offering attractive perspectives, since they represent an important pool of germ cells for women undergoing IVM cycles, or at risk of infertility for OHSS or PCOs, particularly those poor responders to gonadotropin stimulation, or in case of cancer. Therefore, it becomes necessary to optimize both cryopreservation technique as well as in-vitro maturation condition for GV oocytes. Our recent study showed that GV appears more suitable to vitrification than MII, as indicated by the good ultrastructural preservation of important structures that are present only in GVs, like the nucleus and migrating cortical granules (CGs). Also, with PI/Hoechst immunostaining technique, the oocyte viability rate was shown to reduce in vitrified GV (56.0%), when compared with fresh samples (86.8%). In addition, it has been revealed that upon supplementation of the IVM culture media with GDF-9 as an oocyte-secreted GF, resulted in 66.1% of maturation rate and 55.3% of good embryo development. It, however, has to be noted that both stress and apoptosis related genes as assessed by real time PCR, increased post vitrification of human immature oocytes. The differential expression of these genes profile may be useful to evaluate the outcome of these germ cells after cryopreservation. The optimization of a clinical protocol allowing immature oocytes retrieval, that can be matured in vitro after successful vitrification, would offer a significative opportunity for fertility preservation.