1. Department of Family and Community Medicine, University of Illinois at Chicago, Chicago, Illinois, USA.
2. Reproductive Statistics Branch, National Center for Health Statistics, Division of Vital Statistics, Centers for Disease Control and Prevention, Hyattsville, Maryland, USA.
3. Department of Obstetrics, Gynecology and Reproductive Sciences, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA.
4. Epidemiology and Applied Research Branch, Division of Cancer Prevention and Control, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
5. Department of Obstetrics, Gynecology and Reproductive Sciences, Center for Healthcare Value, University of California San Francisco, San Francisco, California, USA.