IUI can be used to treat infertility when tubes are normal, with no severe endometriosis and enough motile spermatozoa can be inseminated. In these cases IUI are usually performed (4 to 6 attempts) and IVF only in case of IUI failure. Indeed if the pregnancy rate per attempt is higher with IVF, IUI can be performed more frequently (6 times a year vs. 2 for IVF) so that the pregnancy rates after one year of treatment are close. When female age is over 37 years, some ART centers prefer to perform directly IVF, since chances of pregnancy decreases with time. However there is no argument in the literature in favor as well as in disfavor for such an attitude. Indeed the delivery rates after one year treatment with IUI or IVF are not known in this population. Therefore we propose a multicentric randomized controlled trial comparing IUI and IVF in women over 37 with unexplained infertility. Couples will be randomly allocated to IUI or IVF during one year. In case of absence of pregnancy after 4 IUI, couples will be treated by IVF. ART attempts will be performed according to usual procedures of each center. The follow-up will be ended either at the end of the first year of treatment if no pregnancy is obtained or at the time of delivery if a pregnancy is obtained. All data of attempts (demographics data, type and doses of treatment, adverse effects, outcome, number and health state of newborns....) will be recorded.