In vitro maturation of oocytes for fertility preservation: a comprehensive review

The development of oncofertility over the past decade has renewed the interest in in vitro maturation (IVM) because of the specificity of some oncologic situations that may prevent the feasibility of controlled ovarian hyperstimulation. Immature cumulus-oocyte complexes can be recovered from the small antral follicles in any phase of the menstrual cycle within a very short time frame, offering the possibility of vitrifying mature oocytes or embryos after IVM in urgent situations or when stimulation is contraindicated. Cumulus-oocyte complexes and immature oocytes can be harvested either transvaginally or directly in the laboratory from extracorporeal ovarian tissue. Although IVM is no longer considered experimental as a result of safety studies, it relies on the extremely complex process of oocyte maturation. Despite some live births obtained after IVM in the context of fertility preservation, the lower developmental competence of in vitro–matured oocytes demonstrates the need to improve IVM culture systems. Recent advances in IVM systems may improve oocyte competence after IVM, thus tending to reduce the gap between IVM and ovarian stimulation outcomes. Moreover, to optimize the chances of conception in cancer survivors, the combination of IVM and ovarian tissue cryopreservation is the preferred option when ovarian stimulation cannot be performed.