Twenty-four studies7- 9,11,19- 31,33- 35,37,38,40,41 reported using oral anticoagulants, most commonly warfarin (Coumadin), throughout pregnancy (regimen 1). Twelve studies9,22,24,28,30,32,34- 36,38,39,42 reported the substitution of heparin in the first trimester of pregnancy (regimen 2). Five studies19,20,26,38,41 reported management of some of these pregnancies with heparin alone throughout pregnancy (regimen 3); in 2 studies19,20 adjusted-dose heparin was used, but the target activated partial thromboplastin time was not reported, and in 3 studies,26,38,41 low-dose heparin (≤15,000 U/d) was used. Seven studies8,11,20,23,24,33,41 reported no anticoagulation use throughout pregnancy, and 2 studies35,41 reported the use of antiplatelet agents only, consisting of aspirin and dipyridamole. Twenty studies8,9,19- 22,24,26- 31,33- 35,37,38,40,41 reported switching to heparin for labor and delivery. Target prothrombin times were reported in 13 studies; these varied from international normalized ratios of 2.0 to 4.0, to prothrombin time ratios of 1.5 to 2.5.