Paradoxical ovarian stimulations in the use of LHRH analogs.

In the case of in vitro fertilization, LHRH analogs are used to induce an hypophysary blockage, before the phase of stimulation, via administration of exogenous gonadotropin. During in vitro fertilization attempts using LHRH analogs, the blockage is controlled after 14 days of treatment through measurement of the plasmatic estradiol and pelvic ultra-sonography. In this retrospective study, which concerned 1075 in vitro fertilization cycles, a paradoxical ovarian stimulation with LHRH analogs was observed in 93 cases (8.7%), with high estradiol levels and follicular growth (detected by ultra-sonography), in spite of low FSH and LH levels. In 4 cases, a follicular puncture was performed, which allowed to collect oocytes from which embryos were obtained, thus confirming the observed follicular growth and maturation. The most probable hypothesis explaining this phenomenon seems to be a direct ovarian stimulation, effectuated in vivo by LHRH analogs. This stimulation is only observed in certain patients, and apparently more frequently, with certain LHRH analogs, probably through a variation in the expression of ovarian LHRH receptors.