1. Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco
2. Department of Epidemiology and Biostatistics, University of California, San Francisco
3. Department of Obstetrics and Gynecology, Massachusetts General Hospital, Boston
4. Marin Community Clinic, San Rafael, California
5. California Pacific Medical Center, San Francisco
6. Feinberg School of Medicine, Department of Obstetrics and Gynecology, Northwestern University, Chicago, Illinois