OBJECTIVE: To assess the safety of using single complete compression ultrasonography in pregnant and postpartum women to rule out deep vein thrombosis. DESIGN: Prospective outcome study. SETTING: Two tertiary care centres and 18 private practices specialising in vascular medicine in France and Switzerland. PARTICIPANTS: 226 pregnant and postpartum women referred for suspected deep vein thrombosis. METHODS: A single proximal and distal compression ultrasonography was performed. All women with a negative complete compression ultrasonography result did not receive anticoagulant therapy and were followed up for a three month period. MAIN OUTCOME MEASURES: Symptoms of venous thromboembolism, second compression ultrasonography or chest imaging, a thromboembolic event, and anticoagulant treatment. RESULTS: 16 women were excluded, mainly because of associated suspected pulmonary embolism. Deep vein thrombosis was diagnosed in 22 out of the 210 included women (10.5%). 10 patients received full dose anticoagulation despite a negative test result during follow-up. Of the 177 patients without deep vein thrombosis and who did not receive full dose anticoagulant therapy, two (1.1%, 95% confidence interval 0.3% to 4.0%) had an objectively confirmed deep vein thrombosis during follow-up. CONCLUSIONS: The rate of venous thromboembolic events after single complete compression ultrasonography in pregnant and postpartum women seems to be within the range of that observed in studies in the non-pregnant population. These data suggest that a negative single complete compression ultrasonography result may safely exclude the diagnosis of deep vein thrombosis in this setting. TRIAL REGISTRATION: clinicaltrials.gov NCT00740454.