1. Epidemiology Branch, National Institute of Environmental Health Sciences, Durham, North Carolina 27709, United States
2. Department of Epidemiology, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina 27599, United States
3. Curriculum in Toxicology and Environmental Medicine, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina 27599, United States
4. Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland 20892, United States
5. Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia 30341, United States
6. Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Eastern Virginia Medical School, Norfolk, Virginia 23507, United States
7. Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston, Texas 77555, United States