1. Department of Public Health Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina, and at the North Carolina Birth Defects Monitoring Program, State Center for Health Statistics, Division of Public Health, Raleigh, North Carolina.
2. Department of Maternal and Child Health, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, and at the Department of Epidemiology, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
3. North Carolina Birth Defects Monitoring Program, State Center for Health Statistics, Division of Public Health, Raleigh, North Carolina, and at the Department of Maternal and Child Health, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.