After randomization at first prenatal visit patients will be allocated to aspirin-enoxaparin or aspirin alone as mentioned above. Enoxaparin will be stopped the day of delivery or after the occurrence of a complication that necessitates delivery. Pregnancy management will be performed as recommended by standard care. Each month, blood samples will be drawn for platelets count and the analysis of angiogenic factors (sFlt1, sEng, free PlGF and VEGF). In addition, blood sample will be drawn at first prenatal visit for thrombophilia work-up (Prot C, Factor V Leiden, Prothrombin gene polymorphism). Only results of platelet count will be given to local investigators during the study. All other analysis will be performed at the end of the study by Pr Gris at NIMES, and will be blinded to clinical results.