[GnRH agonists versus antagonists during in vitro fertilization].

During in vitro fertilization (IVF) GnRH antagonists or agonists are used to optimize the control of organization of oocyte collection. The choice of stimulation protocol also takes into account the ovulatory, clinical, biological and ultrasound characteristics of the FIV candidate, as well as any stimulation measures already taken. Age appears to be the major predictive factor of oocyte response to stimulation and ultrasonography on the 3rd day is a predictive element of the success of oocyte collection. Determination of hormonal parameters on the 3rd day of the cycle (FSH, oestradiol, inhibin B, anti-mullerian hormone) makes it possible to refine the choice of therapy. All these elements are used to define various categories of patients in terms of response to hormonal stimulation. Agonists induce a suppression of pituitary secretion which inhibits the preovulatory LH peak and blocks natural ovulation. Nevertheless, there is an initial transient stimulating effect (flare-up) for a few days and a risk of prolonged ovarian desensitization responsible for side effects. The antagonists, administered just before the supposed ovulatory phase, provoke a rapid diminution in LH while avoiding the flare-up and prolonged ovarian desensitization. Various meta-analyses to compare both types of treatments currently suggest that agonists are superior in terms of number of oocytes produced, though the percentage of mature oocytes obtained as well as the levels of fertility are comparable whatever the type of treatment. In practice, organization of stimulation protocols using agonists is easier especially for teams working in a sequential manner. However, protocols using antagonists may be particularly useful in poor responders and are globally better tolerated.