1. Medical Birth Registry of Norway; Division of Epidemiology; Norwegian Institute of Public Health; Bergen Norway
2. Department of Global Public Health and Primary Care; University of Bergen; Bergen Norway
3. Epidemiology Branch; National Institute of Environmental Health Services; NC USA
4. Division of Public Relations and Institute Resource; Norwegian Institute of Public Health; Bergen Norway
5. Department of Epidemiology; Gillings School of Global Public Health; University of North Carolina; Chapel Hill NC USA
6. Division of Infectious Disease Control; Norwegian Institute of Public Health; Oslo Norway
7. The Mother and Child Cohort Study; Norwegian Institute of Public Health; Oslo Norway