1. Departments of Public Health, Section of Epidemiology and
2. Perinatal Epidemiology Research Unit, Department of Pediatrics, Aarhus University Hospital, Aarhus, Denmark; and
3. National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, Georgia
4. Public Health, Section of Biostatistics, University of Aarhus, Aarhus, Denmark;