Implications of polycystic ovary syndrome on oocyte development.

Human follicle development requires the recruitment of primordial follicles into a cohort of growing follicles from which one follicle is selected to ovulate a mature oocyte. During this developmental process, complex endocrine and intraovarian paracrine signals create a changing intrafollicular hormonal milieu. With this microenvironment, appropriate cumulus cell-oocyte signaling governs oocyte developmental competence, defined as the ability of the oocyte to complete meiosis and undergo fertilization, embryogenesis, and term development. Many of these mechanisms are perturbed in polycystic ovary syndrome (PCOS), a heterogeneous syndrome characterized by ovarian hyperandrogenism, hyperinsulinemia from insulin resistance, and reduced fecundity. In addition to these endocrinopathies, PCOS also is characterized by paracrine dysregulation of follicle development by intraovarian proteins of the transforming growth factor-beta family. Consequently, PCOS patients undergoing ovarian stimulation for in vitro fertilization are at increased risks of impaired oocyte developmental competence, implantation failure, and pregnancy loss. Recent data demonstrate links between endocrine/paracrine factors and oocyte gene expression in PCOS and suggest that new clinical strategies to optimize developmental competence of PCOS oocytes should target correction of the entire follicle growth and oocyte development process.