In an attempt to identify the best treatment for pregnant women with cardiac-valve prostheses who are receiving oral anticoagulants, we studied 72 pregnancies prospectively. In 23 pregnancies (Group I), the coumarin derivative acenocoumarol was discontinued and the patients received 5,000 U of subcutaneous heparin every 12 hours from the 6th to the 12th week of gestation, in 12 pregnancies (Group II), heparin was not substituted for the coumarin derivative until after the 7th week, and in 37 pregnancies, detected after the first trimester (Group III), the coumarin derivative was given throughout gestation. In most patients heparin was again substituted for the oral anticoagulant after the 38th week. Three mothers had thrombosis of a tilting-disk mitral prosthesis (two cases were fatal) during heparin treatment. No differences were found in the rates of spontaneous abortion in the three groups. Coumarin embryopathy occurred in 25 percent and 29.6 percent of the pregnancies in Groups II and III, respectively. We conclude that in the second and third trimesters of pregnancy, coumarin derivatives provide effective protection against thromboembolism while causing few fetopathic effects, but that these agents are contraindicated from the 6th to the 12th weeks of gestation. Low-dose heparin does not protect against prosthetic-valve thrombosis, and the possibility that a larger dose might be more effective requires further exploration.

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