1. Department of Pediatrics, Rikshospitalet University Hospital, Oslo, Norway
2. Department of Pediatric Intensive Care, Ullevål University Hospital, Oslo, Norway
3. Department of Pediatrics, Haukeland University Hospital, Oslo, Norway
4. Department of Pediatrics, St Olav's University Hospital, Trondheim, Norway
5. Department of Pediatrics, University Hospital of Northern Norway, Tromsø, Norway
6. Medical Birth Registry of Norway, Bergen, Norway