Laila Kristoffersen1,2, Ragnhild Støen1,2, Håkon Bergseng1,2, Turid Follestad3, Elvar Theodorsson4, Bente Vederhus5,6, Lars Adde2,7, Dordi Austeng8,9. 1. Department of Neonatology, St. Olavs University Hospital, Trondheim, Norway. 2. Department of Clinical and Molecular Medicine, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. 3. Department of Public Health and Nursing, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. 4. Faculty of Health Sciences, Division of Microbiology and Molecular Medicine, Department of Clinical and Experimental Medicine, Department of Clinical Chemistry, Center for Diagnostics, Linköping University, Region Östergötland, Sweden. 5. Department of Pediatrics, Haukeland University Hospital, Bergen, Norway. 6. Faculty of Health and Social Science, Western Norway University of Applied Sciences, Bergen, Norway. 7. Clinic of Clinical Services, St. Olavs Hospital, Trondheim University Hospital, Trondheim, Norway. 8. Department of Neuromedicine and Movement Science (INB), Norwegian University of Science and Technology (NTNU), Trondheim, Norway. 9. Department of Ophthalmology, St. Olavs University Hospital, Trondheim, Norway.