Failure of low molecular-weight heparin in the prevention of prosthetic mitral valve thrombosis during pregnancy: case report and a review of options for anticoagulation.

All mechanical heart valves are thrombogenic and may be associated with thromboembolic complications if anticoagulation is inadequate. This risk is increased in pregnancy due to a hypercoagulable state. The ideal anticoagulation regimen in pregnant patients with prosthetic heart valves is uncertain. Oral dicoumarol anticoagulants, subcutaneous low molecular-weight heparin, subcutaneous high-dose heparin and continuous high-dose intravenous heparin each have their own merits and demerits. A case is presented of a pregnant patient who had prosthetic valve thrombosis while receiving low molecular-weight heparin and who required re-do prosthetic mitral valve replacement. An analysis is also included of the options available for anticoagulating this difficult patient group.