Effects of in-vivo and in-vitro environments on the metabolism of the cumulus-oocyte complex and its influence on oocyte developmental capacity

There has been an improvement in the blastocyst rates achieved following in-vitro embryo production that can largely be attributed to improved embryo culture conditions based on an increased knowledge of the in-vivo environment, as well as the metabolic needs of the embryo. Despite this, in-vitro oocyte maturation (IVM) conditions have remained largely unchanged. Within the antral follicle, numerous events affect oocyte maturation and the acquisition of developmental competency, including: interactions between somatic cells of the follicle (in particular cumulus cells) and the oocyte; the composition of follicular fluid; and the temperature and vascularity of the follicular environment. Many of these factors change with follicle size and oocyte growth. In contrast, culture conditions for IVM are based on somatic cells that often do not reflect the follicular environment, and/or have complex compositions or additives such as macromolecule supplements that are undefined in nature. Metabolites included in media such as glucose, pyruvate, oxygen and amino acids have been shown to have differential influences on oocyte maturation and competency. Manipulation of these factors and application of gained knowledge of the in-vivo environment may result in improved in-vitro oocyte maturation and overall in-vitro embryo production.