Enrollment and outcomes. The enrollment and outcomes of participants in the trial are shown. In the anticoagulant group, 4 of the 15 withdrawals occurred after an adverse event (1 with a new diagnosis of von Willebrand disease, 2 with unrelated antepartum hemorrhage, and 1 with gastric symptoms). Of the 15 who withdrew, 10 received therapy until at least 12 weeks of gestation. In the surveillance-only group the 3 who received anticoagulant prophylaxis/treatment did so from 6, 16, and 26 weeks, respectively. The 2 who withdrew from surveillance did so at 10 and 24 weeks.