1. Clinical Epidemiology Unit, Department of Medicine, Karolinska University Hospital, Stockholm, Sweden
2. Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark
3. Department of Public Health and Caring Sciences, Uppsala University, Uppsala, Sweden
4. Department of Molecular Medicine and Surgery and
5. Division of Pediatric Surgery, Department of Women and Child Health, Karolinska Institutet, Stockholm, Sweden