STIMULATIONS DE L'OVULATION: UNE NOUVELLE APPROCHE BASEE SUR DES DONNEES PHYSIOLOGIQUES ET CLINIQUES RECENTES. PERSPECTIVES D'AVENIR

Taking into account the experience gained in medically assisted conception and ovulation induction, the pregnancy rate and more particularly the baby home rate after ovarian stimulation protocols remain stable. Today, could we expect to improve our results from our recent knowledge on the role of the different factors involved in the follicular maturation process and ovulation? The improvement of our results means to mimic or to amplify the ovarian physiology, taking into account the FSH actions, the key hormone for follicular maturation. At the beginning of the menstrual cycle, FSH is responsible of the 'rescue' of one or more follicles selected for ovulation, of their growth and their differentiation allowing the evolution of an androgen intrafollicular environment toward an estrogen intrafollicular environment which is necessary for a good quality. In late follicular phase, whereas FSH is acting continuously on the multiplication and differentiation of granulosa cells, in particularly on the stimulation of the aromatase activity, small quantities of LH (included between 1 and 6-8* IU/L) allow final follicular maturation (androgen production, synergical action with FSH and antagonist action on FSH action). It, low dose of LH complements FSH action in final follicular maturation process, high levels (>6-8 IU*/l) are deleterious for follicle or oocyte quality. Numerous studies demonstrate a significant correlation between high levels of LH and the lack of pregnancy either the follicle is submitted to high concentrations at the beginning, at mid or at the end of follicular phase. Recent studies also demonstrated, that high levels of LH were not exclusively associated with an ovarian pathology: these studies show an iatrogenic origin of the increase of LH (with clomiphene citrate or hMG). Finally, in addition of its action on follicular maturation, FSH reduces LH levels and is responsible of a lower estradiol concentration than those observed with hMG. Thus, to mimic or amplify the ovarian physiology, taking advantage of FSH action and keeping physiological LH levels at the same time, allow us to improve the results of our stimulations and, to become more familiar with tomorrow's products: products which will be purer and purer, including only one active principle: FSH or LH.