Hello! Welcome and thank you for asking on HCM! I understand your concern and would explain that pregnancy in women with mechanical valve prostheses has a high maternal complication rate including valve thrombosis and death. The use of warfarin throughout pregnancy carries a risk of embryopathy of about 6%; This risk is possibly lower with a warfarin dose Substitution of warfarin with un-fractionated or low-molecular-weight heparin from the 6th to the 12th week of pregnancy eliminates the risk of embryopathy. Anyway warfarin appears to be safer for the mother with a lower incidence of thromboembolic events than unfractionated or low-molecular-weight heparin. So you should make the decision to continue on warfarine, which is more safe but carries 6% risk of possible fetal abnormalities, or start subcutaneous heparin which is more safe for the baby, but not as safe for you. Regarding anticoagulation, required dosages during pregnancy for all anticoagulants can differ from dosages outside pregnancy. The risk of valve thrombosis with unfractionated or low-molecular-weight heparin is probably lower when aggressive dose-adjustment takes place, based on monitoring of APTT or anti-Xa levels; They may need to be administered 3 times daily, because the increase of glomerular filtration. Hope to have been helpful! Best regards, Dr. Iliri