Pregnancy is associated with an increased risk of venous thromboembolism, which probably varies according to the presence of single or multiple thrombophilic defects. Acquired or inherited thrombophilia is moreover associated with adverse outcomes in pregnancy. For this reason, in the past, pregnant women at risk of venous thromboembolism or pregnancyes have been treated with oral anticoagulants or unfractionated heparin. Both of them are associated with fetal or maternal side effects. Low-molecular-weight heparins (LMWHs) offer several advantages, but they have no or only partial indication for use in pregnancy in many countries. We have prospectively evaluated 114 patients and overall 130 pregnancies treated with prophylactic or therapeutic LMWHs from January 2004 to February 2007. The occurrence of allergic reactions, hemorrhagic episodes, low platelet count, pathological fractures, thromboembolic events and adverse outcomes in pregnancy were considered. There was a significant difference in pregnancy outcome following prophylaxis with LMWHs (chi2 P < 0.0001) and the absolute and the relative risks were significantly decreased in the patients with treated pregnancy compared with those with previous untreated pregnancies. Moreover, in our series of patients, the long-term use of LMWH in pregnancy was confirmed well tolerated, with the rate of adverse effects, though very low, comparable with that in literature. Our experience confirms the safety and the efficacy of LMWH but suggests the need of randomized controlled trials.