The identified main causes of inherited thrombophilia are deficiencies of antithrombin (AT), protein C, or protein S, resistance to activated protein C associated with Factor V Leiden mutation, mutant factor II, and inherited hyperhomocysteinemia. For women from symptomatic families, these defects may be associated with an increased risk of venous thrombosis during pregnancy and/or recurrent fetal loss. Inherited thrombophilia is common and appears to be a multigenic disorder. The thrombotic risk seems to be greatest for women who have AT deficiency or more than one thrombophilic defect. The abnormalities that are now recognized are only part of the genetic predisposition to thrombosis. When assessing thrombotic risk during pregnancy, acquired risk factors as well as genetic predisposition should be considered. Increasing age, obesity, immobility, and delivery by cesarean section are major acquired risk factors. Pregnancy should be planned as far as possible, and each patient should be managed individually. During pregnancy, heparin is the anticoagulant of choice, and treatment with warfarin should be avoided because of risks for the fetus. When patients receive long-term treatment with warfarin, pregnancy should be avoided or planned, and warfarin should be discontinued before conception or as soon as pregnancy is confirmed and before 6-weeks' gestation. For women who have AT deficiency, the incidence of thrombosis during pregnancy is between 20 and 40%. Adjusted-dose heparin throughout pregnancy is recommended, followed by warfarin for at least 3 months postpartum. For patients who have Factor V Leiden, mutant factor II, or a deficiency of protein C or protein S, treatment can be based on personal and family history. Thromboprophylaxis during late pregnancy and postpartum should be considered. Fetal loss may be increased for women with inherited thrombophilia. The risk appears to be greatest for women with AT deficiency and women with more than one thrombophilic defect. For women with recurrent fetal death and inherited thrombophilia, a number of case reports claim that prophylaxis with heparin during pregnancy has resulted in successful pregnancy.