Acute thrombosis of a prosthetic mitral valve in pregnancy in spite of adjusted-dose low-molecular-weight heparin and aspirin.

A 31-year-old primigravida had a 27-mm CarboMedics mitral valve implanted previously for mitral regurgitation. The patient had decided to take low-molecular-weight heparin (LMWH) and aspirin throughout her pregnancy. Monthly echocardiography and anti-Factor Xa levels were satisfactory. She presented at 36 weeks' gestation with 24 h of exertional dyspnea, and was in pulmonary edema. Transthoracic echocardiography suggested valve thrombosis. The patient underwent mitral valve replacement after the vaginal delivery of a healthy infant. The resected valve was found to have adherent fresh thrombus. The recent recommendation that LMWH plus aspirin might provide adequate anticoagulation for mechanical valves in pregnancy does not prevent acute prosthetic mitral valve thrombosis.