1. Division of Research, Palo Alto Medical Foundation Research Institute, Palo Alto, California
2. Department of Obstetrics and Gynecology, Palo Alto Medical Foundation, Palo Alto, California
3. Department of General Medical Disciplines, Stanford University School of Medicine, Stanford, California
4. Department of Health Research and Policy, Stanford University School of Medicine, Stanford, California
5. Department of Obstetrics and Gynecology, Vanderbilt University, Nashville, Tennessee