1. Department of Obstetrics and Gynecology, University of Massachusetts Medical School Baystate Medical Center, Springfield, MA, USA
2. Physicians and Midwife Collaborative Practice, Arlington, VA, USA
3. Office of Research, Epidemiology/Biostatistics Research Core, Baystate Medical Center, Springfield, MA, USA
4. Department of Medicine, University of Massachusetts Medical School - Baystate, Springfield, MA, USA
5. Department of Obstetrics and Gynecology, Thomas Jefferson University Hospital, Philadelphia, PA, USA