1. University of Texas Health Science Center, Houston, Texas.
2. Departments of Obstetrics and Gynecology and Pathology, Duke University Medical Center, Durham, North Carolina.
3. Department of Epidemiology, Boston University School of Public Health, Boston, Massachusetts.
4. Departments of Community and Family Medicine and Pediatrics, Dartmouth Medical School, Lebanon, New Hampshire.
5. Department of Obstetrics and Gynecology, University of Chicago, Chicago, Illinois.
6. Department of Obstetrics and Gynecology, New England Medical Center, Boston, Massachusetts.
7. Department of Obstetrics and Gynecology, Methodist Hospital, Houston, Texas.
8. Department of Obstetrics and Gynecology and Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas.
9. Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas.