1. 1Department of Anesthesiology, Columbia University Vagelos College of Physicians and Surgeons, New York, New York.
2. 2Department of Health Policy and Management, Columbia University Mailman School of Public Health, New York, New York.
3. 3Department of Anesthesiology, Columbia University Vagelos College of Physicians and Surgeons, New York, New York.
4. 4Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, Columbia University Vagelos College of Physicians and Surgeons, New York, New York.
5. 5Department of Anesthesiology, Columbia University Vagelos College of Physicians and Surgeons, New York, New York; Department of Epidemiology, Columbia University Mailman School of Public Health, New York, New York.