A risk of bleeding can be associated with any anticoagulation therapy; however, in pregnant patients, other safety concerns may also need to be considered. The use of unfractionated heparin (UFH) during pregnancy is associated with reduced bone density, vertebral fracture and a small risk of heparin-induced thrombocytopenia (HIT). Low molecular weight heparin (LMWH) use for the treatment or prevention of acute venous thromboembolism (VTE) during pregnancy is associated with adverse events including arterial thrombosis, osteoporosis, bleeding and allergic skin reactions. Adverse events such as HIT, bleeding and osteoporosis have been shown to occur at a lower frequency in patients receiving LMWHs compared with those receiving UFH. Vitamin K antagonists (VKAs) are not recommended during pregnancy.