1. Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland 20892
2. Department of Obstetrics and Gynecology, University of Utah and Intermountain Healthcare, Salt Lake City, Utah 84132-2209
3. Centers for Financing, Access and Cost Trends, Agency for Healthcare Research and Quality, Rockville, Maryland 20857
4. Department of Clinical Sciences, Obstetrics and Gynecology, Geisinger Commonwealth School of Medicine, Scranton, Pennsylvania 18509
5. Department of Statistics, University of Haifa, Haifa 3498838, Israel
6. Department of Epidemiology and Environmental Health, University at Buffalo, Buffalo, New York 14214-8001
7. Department of Family and Preventive Medicine, University of Utah, Salt Lake City, Utah 84108