Objective: To determine whether predefined maternal early warning triggers (MEWTs) can predict pregnancy morbidity. Methods: In a retrospective case-control study, obstetric patients admitted to the intensive care unit (ICU) between 2012 and 2013 at seven pilot US hospitals were compared with control patients who had a normal delivery outcome. Six MEWTs were assessed. Results: The case and control groups each contained 50 patients. Hemorrhage (15/50, 30%), sepsis (12/50, 24%), cardiac dysfunction (8/50, 16%), and pre-eclampsia (6/50, 12%) were the most common reasons for ICU admission. Significant associations were recorded between ICU admission and tachycardia (OR 5.0, 95% CI 2.1-11.7), mean arterial pressure less than 65 mm Hg (OR 4.5, 95% CI 1.9-10.8), temperature of at least 38 degrees C (OR 44.1, 95% CI 13.0-839.1), and altered mental state (OR 44.1, 95% CI 13.1-839.0). Two or more triggers were persistent for 30 minutes or more in 36 (72%) ICU patients versus 2 (4%) controls (OR 61.7, 95% CI 13.2-288.0). Earlier medical intervention might have led to a lesser degree of maternal morbidity for 31 (62%) ICU patients with at least one MEWT. Conclusion: Persistent MEWTs were present in most obstetric ICU cases. Retrospectively, MEWTs in this cohort seemed to separate normal obstetric patients from those for whom ICU admission was indicated; their use might reduce maternal morbidity. (C) 2015 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved.