1. Department of Obstetrics and Gynecology, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina
2. Ariadne Labs, Brigham and Women's Hospital, Boston, Massachusetts
3. Department of Obstetrics and Gynecology, Thomas Jefferson University, Philadelphia, Pennsylvania
4. Department of Health Policy and Management, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina
5. Department of Obstetrics and Gynecology, Jefferson Abington Hospital, Abington, Pennsylvania
6. Department of Obstetrics and Gynecology, Newton-Wellesley Hospital, Newton, Massachusetts
7. Department of Obstetrics and Gynecology, Kaiser Permanente, Northern California, San Francisco, California