Henri Aarnivala1,2, Arja Harila-Saari3, Riitta Niinimäki4,5. 1. Department of Children and Adolescents, Oulu University Hospital, Oulu, Finland. henri.aarnivala@oulu.fi. 2. PEDEGO Research Unit, University of Oulu, Oulu, Finland. henri.aarnivala@oulu.fi. 3. Department of Women's and Children's Health, Uppsala University Hospital, Uppsala, Sweden. 4. Department of Children and Adolescents, Oulu University Hospital, Oulu, Finland. 5. PEDEGO Research Unit, University of Oulu, Oulu, Finland.