Improving in vitro maturation of oocytes in the human taking lessons from experiences in animal species

One to three per cent of infertile women develop severe ovarian hyperstimul ation syndrome after superovulation for assisted reproduction treatment (AR T). This severe complication can be avoided when oocytes are obtained at an immature stage (germinal vesicle stage) out of small or medium-sized folli cles. This hypothesis has been tested in several infertile women, but clini cal pregnancies are disappointlingly low. This new approach in ART is still at an experimental phase and this treatment has still to be improved befor e routine clinical application. Experimental work in animals and humans sug gest a beneficial effect in providing a short preliminary pretreatment with follicle-stimulating hormone to select for a developing cohort of follicle s. The aspiration of oocyte cumulus complexes is carried out with a short n eedle applying reduced aspiration pressure. A crucial point is to provide t he appropriate culture environment for the immature oocytes. An optimal cum ulus-enclosed human oocyte culture system needs to be defined. The composit ion of the culture medium could be suggested by in vitro work carried out i n animal models. As developmental competence is established during the late st phases of oocyte growth and is dependent on the storage of RNA, a prolon ged in vitro maturation period (before inducing nuclear maturation) could p rovide the necessary transcriptional and translational changes. The conditi ons to achieve this improved cytoplasmic maturation by prolonging the in vi tro culture remain to be defined. More objective noninvasive parameters for oocyte maturity are also needed to pursue research in this field.