Contributions of in vitro fertilization to knowledge of the reproductive endocrinology of the menstrual cycle.

The administration of ovarian stimulants to endocrine-normal women in IVF programmes gives the clinical endocrinologist an opportunity to modify natural folliculogenesis. Use of antioestrogens and/or gonadotrophins at the correct time has demonstrated that follicular atresia can be prevented and that multiple pregnancy-potent haploid ova can be obtained. Scrutiny of spontaneous menstrual cycles in patients who show unsatisfactory IVF responses has identified two new syndromes, premature follicle selection and occult ovarian failure, in these patients. The incidence of these disorders in fertile women is still unclear. Early results suggest that endocrine manipulations may overcome premature follicle selection and induce codominant folliculogenesis. Inhibin is a recently characterized ovarian protein which is increased in peripheral blood during IVF treatment. Results from IVF cycles suggest that plasma inhibin may be a new index of follicular function. Other potential indices of ovarian function, such as the luteal protein relaxin, may also develop from the application of basic research to IVF and advance knowledge of the human ovarian and menstrual cycles.