In some patients with mechanical prostheses, ingrowth of a fibrous pannus can impede blood flow and lead to hemodynamic stenosis, requiring reoperation. Problems Associated with Pregnancy Pregnancy is contraindicated in women with mechanical prostheses because of considerable risk to mother and fetus. If possible, valve repair or insertion of an allograft or an autograft should be attempted in a woman of childbearing age who wishes to become pregnant. Xenografts have a reduced durability in young patients, especially during pregnancy, and are best avoided. The management of patients with mechanical prostheses who become pregnant or who desire pregnancy is controversial.
Warfarin is associated with an embryopathy and increases the risk of fetal wastage.
Optimal anticoagulation is also difficult with heparin, especially when given by the subcutaneous route, and is associated with increased maternal risk for thromboembolism and hemorrhage. This approach involves administering heparin every 12 hours and keeping the activated partial thromboplastin time at 1.5 to 2.0 times the control value six hours after administration.