1. Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland
2. Biostatistics Research Branch, Division Clinical Research, National Institute of Allergy and Infectious Diseases, Fishers Lane, Rockville, Maryland
3. Department of Obstetrics and Gynecology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois
4. Department of Obstetrics and Gynecology, Medical University of South Carolina, Charleston, South Carolina
5. Department of Obstetrics and Gynecology, The University of Alabama at Birmingham Center for Women's Reproductive Health, Birmingham, Alabama
6. Department of Obstetrics-Gynecology, Division of Maternal-Fetal Medicine, University of California, Irvine, School of Medicine, Orange, California
7. Miller Children's Hospital/Long Beach Memorial Medical Center, Long Beach, California
8. Biostatistics Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, Maryland