This chapter has focused on the step-down principle for gonadotrophin induction of ovulation in women suffering from clomiphene-resistant anovulation. The physiological rationale of this approach has been highlighted. Under normal conditions, FHS levels surpassing the FSH threshold initiate gonadotrophin-dependent growth of a cohort of follicles (this process is referred to as 'recruitment'). Due to negative feedback actions, the FSH levels decrease and FSH is above the threshold for only a limited number of days (the 'FSH window'). Around the mid-follicular phase, selection of a dominant follicle takes place; in addition to relatively low serum FSH concentrations, intraovarian regulation appears to be important for this process. In the conventional step-up or low dose step-up protocols for gonadotrophin induction of ovulation, administered doses are kept constant once an 'adequate' ovarian response is observed, resulting in high FSH serum levels in the late follicular phase and a broad FSH window. This contradicts normal circumstances and may give rise to unintended interference with the selection process by continuously stimulating follicles to enter the growing pool. This may result in multiple follicle development which, in turn, may be related to higher rates of multiple pregnancies and ovarian hyperstimulation. Potential mechanisms underlying arrested follicle maturation in PCOS are also discussed since they appear to be of relevance for the induction of ovulation. Disturbed selection can be overcome in the majority of cases by elevating the serum FSH concentrations through the administration of exogenous gonadotrophins to surpass the elevated FSH threshold in these patients. Data obtained by our group so far suggest that in PCOS patients treated with gonadotrophins in a step-down fashion, follicles continue to mature and can be stimulated to ovulation. Moreover, the number of functionally active medium-sized follicles seems to be reduced. If monofollicular development is observed in these patients, growth rates and oestrogen serum levels are indistinguishable from unstimulated normal development of the dominant follicle. In our initial series of over 200 cycles of gonadotrophin treatment according to the step-down principle in clomiphene-resistant anovulatory patients, 84% of cycles were ovulatory and pregnancy was achieved in 18% of the cycles (giving a cumulative pregnancy rate of 51%). Moreover, the overall complication rate appears to be low. The potential advantages and critical points of adjuvant treatment with GnRH analogues is also discussed. It has been clearly demonstrated that premature luteinization can be prevented effectively. Various other potential advantages of cotreatment seems to justify adjuvant medication with GnRH agonists. However, the beneficial effect of GnRH agonist cotreatment for clinical practice has not (yet) been shown convincingly and therefore it seems that cotreatment should be restricted to those patients who show an inadequate response to gonadotrophins alone. The introduction of GnRH antagonists into clinical practice may further improve treatment outcome. © 1993 Baillière Tindall. All rights reserved.
