1. Division of Epidemiology, Norwegian Institute of Public Health, Oslo, Norway;
2. Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden;
3. Department of Pediatrics, Østfold Hospital Trust, Fredrikstad, Norway;
4. Department of Obstetrics and Gynecology, Norra Älvsborg Hospital, Trollhättan, Sweden; and
5. Department of Pediatrics, Örebro University Hospital, Örebro, Sweden