To assess whether treatment with enoxaparin and low-dose aspirin, along with intensive pregnancy surveillance, reduces rate of pregnancy loss compared with intensive pregnancy surveillance alone in women with history of 2 or more consecutive previous pregnancy losses, a parallel group, multicenter, randomized controlled trial was performed in the United Kingdom and New Zealand. Participants (n = 294) presenting for initial antenatal care at fewer than 7 weeks' gestation with history of 2 or more consecutive previous pregnancy losses at 24 or fewer weeks' gestation and no evidence of anatomic, endocrine, chromosomal, or immunologic abnormality were randomly assigned to receive either enoxaparin 40 mg subcutaneously and 75 mg of aspirin orally once daily along with intense pregnancy surveillance or intense pregnancy surveillance alone from random assignment until 36 weeks' gestation. The primary outcome measure was pregnancy loss rate. Of the 147 participants receiving pharmacologic intervention, 32 (22%) pregnancy losses occurred, compared with 29 losses (20%) in the 147 subjects receiving intensive surveillance alone, giving an odds ratio of 0.91 (95% confidence interval, 0.52-1.59) of having a successful pregnancy with pharmacologic intervention. Thus, we observed no reduction in pregnancy loss rate with antithrombotic intervention in pregnant women with 2 or more consecutive previous pregnancy losses. The trial was registered at http://www.controlled-trials.com as ISRCTN06774126.