In vitro maturation of human oocytes

Maturation of human oocytes has 3 aspects: nuclear maturation leading to th e extrusion of the Ist polar body, membranar maturation essential for the f ixation of spermatozoa to the zona pellucida and penetration into the oocyt e and cytoplasmic maturation which allows protein synthesis required for no rmal fertilisation and embryo development In vitro maturation (IVM) of huma n oocytes may be appropriate in 5 different situations: for PCOs patients ( natural cycle), in normoovulatory patients (natural cycles), for oocytes no t exposed to hCG (stimulated cycle), for immature oocytes recovered in the course of an ICSI protocol (stimulated cycle) and after freezing-thawing of immature oocytes, Data from the literature show that in vitro maturation o f human oocytes together with ICSI can lead to normal fertilisation, embryo development, pregnancies and the delivery of healthy children. However, th e overall efficiency is still very low, indicating that embryo viability is compromised. The incidence of chromosome abnormalities in mature oocytes o btained after IVM is similar to that of oocytes recovered after in vivo mat uration and therefore does not seem to be the reason of the failures. Conve rsely protein synthesis abnormalities and abnormal calcium signalling might explain the poor viability of the embryos. The key factor seems to be cyto plasmic maturation not yet fully understood in the human.