1. Department of Biostatistics National Center on Birth Defects and Developmental Disabilities, Atlanta, GA.
2. Department of Epidemiology National Center on Birth Defects and Developmental Disabilities, Atlanta, GA.
3. Aarhus University Hospital, and the Centers for Disease Control and Prevention National Center on Birth Defects and Developmental Disabilities, Atlanta, GA.
4. Department and Research Unit of General Practice National Center on Birth Defects and Developmental Disabilities, Atlanta, GA.
5. Department National Center on Birth Defects and Developmental Disabilities, Atlanta, GA.