[Therapeutic induction of ovulation: towards the replacement of hCG with LH]

Ovulation has exclusively been triggered with Human Chorionic Gonadotropin (hCG) since the earlier times of follicular stimulation with Pregnant Mare Serum Gonadotropins (PMSG). hCG was chosen in regard of its LH-like effect, when isolated or purified human LH was not available. hCG, however, is not the physiologic hormone for ovulation triggering and shows many discrepancies in pharmacokinetics and bio-availability with LH, accounting for the permanent risk for ovarian hyperstimulation syndrome (OHSS) following hCG administration. Human recombinant LH should become available in the coming years, but it is at present possible to trigger ovulation in hMG--stimulated patients with their own pituitary LH, using a short-acting GnRH agonist. Literature shows that this method of triggering ovulation in in vitro fertilization (IVF) cycles as well as in non IVF cycles results in a satisfactory ovulatory process and pregnancy rates comparable to those observed following hCG administration. More over, triggering ovulation with endogenous LH considerably reduces the risks for OHSS, and perhaps for multiple pregnancies. Optimum posology for each GnRH agonist available remains to be evaluated to minimize the occurrence of short luteal phases following ovulation triggering with endogenous LH.