1. Department of Epidemiology, University of North Carolina, Chapel Hill, North Carolina.
2. Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina.
3. Department of Biostatistics and Carolina Population Center, University of North Carolina, Chapel Hill, North Carolina.
4. Environmental Health Perspectives, National Institute of Environmental Health Sciences, Morrisville, North Carolina.
5. Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, North Carolina.
6. Institute for Medicine and Public Health, Vanderbilt University Medical Center, Nashville, Tennessee.
7. Department of Obstetrics and Gynecology, Vanderbilt University Medical Center, Nashville, Tennessee.