Venous thromboembolic (VTE) complications are a leading cause of maternal mortality in the developed world. To reduce the incidence of VTE in pregnancy, and improve outcomes, a wider understanding of the risk factors involved and a better identification of women at risk of thrombosis coupled with effective thromboprophylaxis and treatment of VTE are required. As coumarin is unsuitable for use in pregnancy because of problems with embryopathy and risk of fetal bleeding, anticoagulation therapy in pregnancy centres on the use of low-molecular-weight heparin (LMWH) and unfractionated heparin (UFH). There is now extensive experience of the safety and efficacy of LMWH in pregnancy. LMWH's, such as enoxaparin and dalteparin, have clinical and practical advantages compared with UFH in terms of improved safety (significantly lower incidence of osteoporosis and heparin induced thrombocytopenia), and patient convenience with once daily dosing for the majority of women. Such therapy is not restricted only to prevention and treatment of VTE but is now being assessed in additional clinical situations such as the prevention of pregnancy complications.