Recruitment prior to ovarian stimulation: ways of improving follicular recruitment.

Modulation of follicle profiles prior to FSH in cycles of assisted reproduction is an important part of current practice, but perhaps with wider applications in the future. The conventional use of gonadotrophin-releasing hormone (GnRH) antagonists has employed the perimenstrual rise in FSH to initiate follicular development from antral stages, leading to two stages of follicular development, endogenously stimulated followed by the exogenously stimulated. This contrasts with GnRH agonists, where there is a single and continuous induction of growth. In theory, it may prove possible to modulate the source material, the antral follicle pool by using LH to sensitize follicles to FSH. However, in polycystic ovary syndrome, with its excessive follicle pool, short-term reduction of insulin promoted LH action by metformin treatment has failed to influence follicle responses to exogenous FSH. On the other hand, there is now evidence that long-term metformin treatment may lead to a reduction in the size of the antral follicle pool, potentially leading to lower risk of ovarian hyperstimulation.