1. Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, Texas
2. George Washington University Biostatistics Center, Washington, District of Columbia
3. Department of Obstetrics and Gynecology, The Ohio State University, Columbus, Ohio
4. Department of Obstetrics and Gynecology, University of Utah Health Sciences Center, Salt Lake City, Utah
5. Department of Obstetrics and Gynecology, Columbia University, New York, New York
6. Department of Obstetrics and Gynecology, Brown University, Providence, Rhode Island
7. Department of Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham, Alabama
8. Department of Obstetrics and Gynecology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
9. Department of Obstetrics and Gynecology, MetroHealth Medical Center-Case Western Reserve University, Cleveland, Ohio
10. Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston, Texas
11. Department of Obstetrics and Gynecology, Northwestern University, Chicago, Illinois
12. Department of Obstetrics and Gynecology, University of Texas Health Science Center at Houston-Children's Memorial Hermann Hospital, Houston, Texas
13. Department of Obstetrics and Gynecology, Medical University of South Carolina, Charleston, South Carolina