1. Section of Social Medicine, Department of Public Health, University of Copenhagen, Copenhagen, Denmark
2. Department of Epidemiology, Fielding School of Public Health, University of California, Los Angeles, CA, USA
3. Cerebral Palsy Register of Norway, Vestfold Hospital Trust, Tønsberg, Norway
4. Section of Biostatistics, Department of Public Health, University of Copenhagen, Copenhagen, Denmark
5. Department of Clinical Epidemiology, Aarhus University, Aarhus, Denmark
6. Pharmacoepidemiology and Risk Management, Research Triangle Institute Health Solutions, Barcelona, Spain
7. Domain for Mental and Physical Health, Norwegian Institute of Public Health, Bergen, Norway
8. Pediatric Department, University Hospital Rigshospitalet, Copenhagen, Denmark
9. Epidemiology Branch, National Institute of Environmental Health Sciences, Durham, NC, USA