Administration of heparin in the secondary prevention of placental vascular complications is still experimental. In women with a previous placental abruption, we investigated the effectiveness of enoxaparin, a low-molecular-weight heparin, in preventing these complications. Between January 2000 and January 2009, 160 women from the NOHA First cohort, with previous abruptio placentae but no foetal loss during their first pregnancy and negative for antiphospholipid antibodies, were randomised to either a prophylactic daily dose of enoxaparin starting from the positive pregnancy test (n=80), or no enoxaparin (n=80). The primary outcome was a composite of at least one of the following: abruptio placentae, preeclampsia, birthweight < 5th percentile, or foetal loss after 20 weeks. Enoxaparin was associated with a lower frequency of primary outcome: 12.5% (n=10/80) vs. 31.3 % (25/80), p=0.004, adjusted hazard ratio = 0.37, 95% confidence interval (0.18-0.77), p=0.011. Enoxaparin was safe, with no obvious side-effect, no thrombocytopenia nor major bleeding event excess. This pilot study shows that enoxaparin given early during the second pregnancy decreases the occurrence of placental vascular complications in women with a previous placental abruption during their first pregnancy.