1. The George Washington University Biostatistics Center, Washington, DC
2. Department of Obstetrics and Gynecology University of Pittsburgh, Pittsburgh, Pennsylvania
3. Department of Obstetrics and Gynecology, University of Cincinnati, Cincinnati, Ohio
4. Department of Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham, Alabama
5. Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, Texas
6. Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, Utah
7. Department of Obstetrics and Gynecology University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
8. Department of Obstetrics and Gynecology, Case Western Reserve University-MetroHealth Medical Center, Cleveland, Ohio
9. Department of Obstetrics and Gynecology, Northwestern University, Chicago, Illinois
10. Department of Obstetrics and Gynecology University of Texas Health Science Center at Houston, Houston, Texas
11. Department of Obstetrics and Gynecology, The Ohio State University, Columbus, Ohio
12. Department of Obstetrics and Gynecology, Drexel University, Philadelphia, Pennsylvania
13. Department of Obstetrics and Gynecology, Oregon Health & Science University, Portland, Oregon
14. Department of Obstetrics and Gynecology, Wayne State University, Detroit, Michigan
15. Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston, Texas