A consensus on the correct anticoagulation regimen during pregnancy is lacking. Treatment is tailored to the particular individual based on her risk of complications. Warfarin and other vitamin K-inhibiting agents are contraindicated during the first trimester of pregnancy because of the teratogenic effects, and should not be administered when the pregnancy is confirmed. Rather, women who are on chronic anticoagulation may be given the option of conversion to either unfractionated heparin or low molecular weight heparin (LMWH), such as tinzaparin, prior to a planned conception. LMWH is as safe and efficacious as unfractionated heparin. A blood test including platelets and a clotting screen should be performed prior to administration of anticoagulant regimens in pregnancy.