In-vitro maturation of oocytes: biological aspects.

Natural cycle and in-vitro maturation (IVM) of oocytes are becoming interesting alternatives to classical assisted reproduction technology approaches for patients, especially in those at high risk for ovarian hyperstimulation syndrome or with poor ovarian reserve. More than for their clinical and biological indications, natural cycle and IVM of oocytes can also be considered as good social and economic alternatives to the classical IVF treatment, based on their financial cost-effectiveness with exclusion of expensive medications. To be successful, IVM must entail both nuclear and cytoplasmic maturation, and its maturation and success rates are affected by the number of collected cumulus layers, the degree of atresia and the maturation rate between 24 and 48 h. Endogenous regulation of oocyte maturation is a complex sequence of events regulated by endocrine parameters, oocyte/follicular cross-talk, and intra-oocyte kinase/phosphatase interactions. This complex process requires a better definition of each contributing factor affecting oocyte development and the resulting embryo quality. The clinical aspects of IVM have been documented earlier; the present paper will mainly focus on the biological aspect of oocyte maturation in vitro and the quality of derived embryos.