Standard investigations fail to reveal any apparent cause in 50% of the cases of recurrent spontaneous abortion. Prothrombotic mechanisms were initially evoked. Factor V Leiden, Prothrombin G20210A mutation and protein S deficiency are implicated in the meta-analysis of Rey (Lancet).However, they do not account for a large number of miscarriages.Gris JC and coworkers (Blood 2004)carried out an open trial, low-molecular-weight heparin versus low-dose aspirin, in women with one fetal loss and with a constitutional thrombophilic disorder. They conclude for a benefit action of Low-molecular-weight heparin. There is actually no trials concerning women with unexplained recurrent abortions and without known thrombophilia. Nevertheless,aspirin or enoxaparin are often prescribed. It is time to assess these practices. We therefore initiate a multisite, double blind randomized study, enoxaparine versus placebo, in women without known thrombophilia, which experienced unexplained recurrent abortions.