1. Department of Laboratory Medicine, Children's and Women's Health, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway;
2. Department of Pediatrics, St. Olavs Hospital/Trondheim University Hospital, Trondheim, Norway;
3. The Cerebral Palsy Registry of Norway, Habilitation Center, Vestfold Hospital, Tønsberg, Norway;
4. Department of Obstetrics and Gynaecology, Clinical Sciences, Lund University, Lund, Sweden;
5. Medical Birth Registry of Norway, Locus of Registry-based Epidemiological Research, Norwegian Institute of Public Health, Oslo, Norway;
6. Department of Public Health and Primary Health Care, University of Bergen, Bergen, Norway; and
7. National Perinatal Epidemiology Unit, University of Oxford, Oxford, United Kingdom