1. Biostatistics Center, The George Washington University, Washington, District of Columbia
2. Department of Obstetrics and Gynecology, University of Cincinnati, Cincinnati, Ohio
3. Department of Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham, Alabama
4. Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, Texas
5. The Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland
6. Department of Obstetrics and Gynecology, Case Western Reserve University-MetroHealth Medical Center, Cleveland, Ohio
7. Department of Obstetrics and Gynecology, University of Texas Medical Center, Galveston, Texas