1. Department of Epidemiology; College of Public Health, The University of Iowa; Iowa City Iowa
2. Genetics and Teratology Unit; Massachusetts General Hospital; Boston Massachusetts
3. National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention; Atlanta Georgia
4. Congenital Malformations Registry, Bureau of Environmental and Occupational Epidemiology; New York State Department of Health; Albany New York