[Ovarian stimulation: a new approach based on recent physiological and clinical data. Future perspectives].

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, synergic action with FSH and antagonist action on FSH action). If, 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.(ABSTRACT TRUNCATED AT 250 WORDS)