Oocyte development: it's all about quality.

Mammalian fertility depends on the production of an oocyte capable of fertilization and supporting early embryo development. This requires both cytoplasmic and nuclear, i.e. chromosomal, competence, processes that were initiated decades prior to ovulation. Current demographic changes with delayed motherhood are increasingly in conflict with these biological processes. This brief review highlights the key stages in oocyte development, as well as recent findings that continue to inform on how the oocyte is able to maintain function over such a prolonged period. These include minimizing oocyte damage caused by the production of reactive oxygen species, the importance of intercellular communication with the surrounding somatic cells, and the molecular mechanisms that underpin the fidelity of chromosome cohesion and then separation at the resumption of meiosis. Some of these are already approaching clinical testing and interventions, with new approaches in the coming years potentially being able to 'put back the clock' to improve oocyte quality.