Anti-Xa Activity with Low-Molecular-Weight Heparin, Enoxaparin, During Pregnancy in Women with Mechanical Heart Valves

Increased risk of venous thromboembolism has been associated with pregnancy. Physiological adaptation for delivery may include an increase in hypercoagulability. High levels of von Willebrand factor, factor VII, factor X, factor VIII, factor V, and fibrinogen, acquired resistance to activated protein C, reduction of protein S and impaired fibrinolysis have been reported during pregnancy. Venous stasis may also augment the risk of venous thromboembolism [1]. Pregnant women with mechanical heart valves are at high risk of thrombosis as all mechanical valves are thrombogenic. Several design modifications have been made in these valves to improve their duration and to reduce thrombogenicity. Nevertheless, thromboembolism remains the major problem for mechanical prosthetic valves and longterm anticoagulation is mandatory to prevent this complication. Controversy exists regarding the appropriate and safe anticoagulation regimen in pregnant patients with these valve prostheses. Coumarin derivatives are effective in preventing thromboembolic phenomena in these patients. However, these agents cross the placental barrier and should be avoided from the 5 th to 13 th weeks of pregnancy