Oocyte in vitro maturation

In the human species oocyte growth from a diameter of 20-30µm up to a variable final oocyte diameter of 115-120µm is achieved mainly during the preantral follicle phase. Regulation of the preantral growth phase is still not very well studied, and by using fertility drugs we cannot intervene with these growth stages. Knowledge on early follicle growth stages was mainly gained from studies in rodent and domestic animal species. These studies showed that oocyte growth and quality are dependent on the normal growth and differentiation of the oocyte’s harboring follicle. However, the oocyte itself also plays a directing part in the follicular environment, for example by preventing premature luteinization by regulating secretion of cumulus mucification enabling factors, luteinizing hormone (LH) receptor expression on cumulus cells and Kit ligand expression in granulosa cells.1-4 Human oocytes obtained for in vitro maturation (IVM) are aspirated from 2-12mm follicles and have not completely fulfilled their growth and final maturation. Previous work has shown that, during the period just preceding the final meiotic maturation stage, synthesis and packaging of RNA and translational products are a very important process determining further developmental events.5-6 When retrieving oocyte cumulus complexes from small antral follicles for IVM it is our aim to substitute for those intrafollicular maturation conditions which seem to be fundamental for further embryonic development. The small antral follicles which are aspirated for the purpose of IVM have already undergone a growth period of several months and have moved into a state of gonadotropin responsiveness.7