Pulmonary embolism and/or deep vein thrombosis are a major cause of maternal mortality. In a number of adverse pregnancy outcome including preeclampsia, recurrent spontaneous abortion, restricted fetal growth and fetal death a role for thrombophilia (acquired and hereditable) has been postulated. Monitoring of acquired factors such as antiphospholipid-antibodies and hereditable factors (factor V Leiden, prothrombin mutation) may help predict the occurrence of pregnancy complications. Low molecular weight heparins (LMWH), since their introduction well established during pregnancy, and the rate of adverse fetal outcomes are related to co-morbidity maternal conditions rather than to the treatment itself. The use of LMWH is recommended for all moderate risk and high-risk pregnant patients.