This chapter addresses the practical obstetric and anesthetic management of women on prophylactic heparin and therapeutic anticoagulation in the peri-partum period, and the dilemmas for obstetricians, anesthetists, and hematologists. It considers issues surrounding use of thrombolytic agents in pregnancy, and unusual but complex situations such as cardiopulmonary bypass in pregnancy. Increasing use of prophylactic anticoagulants in pregnancy, both for venous thromboprophylaxis and to modify fetal risk, as in antiphospholipid syndrome, means that more women are now reaching the peri-partum period on anticoagulants, usually a low molecular weight heparin. The safety in pregnancy of other antiplatelet agents such as clopidogrel or ticlopidine at usual therapeutic doses has not been established and they are rarely used. Most of the women requiring prophylactic doses of anticoagulant will be given one of the low molecular weight heparins (LMWH).