Serum luteinizing hormone during ovulation induction with human menopausal gonadotropin for in vitro fertilization in normally menstruating women.

Sixteen cycles in 14 normally menstruating women, stimulated with human menopausal gonadotropin in order to recruit more than one follicle for a successful in vitro fertilization process, were adequately monitored to identify the appearance of the spontaneous luteinizing hormone (LH) surge. Daily serum LH determinations, increased to every 4 hours in the presumptive preovulatory period, showed that in these women the endogenous estrogen-triggered LH midcycle peak did not occur at the expected time. It is hypothesized that the mechanism responsible for this suppression is a negative feedback mediated by an increased circulating protein with an inhibin-like action.