1. Department of Obstetrics; Rigshospitalet Copenhagen University Hospital; Copenhagen Denmark
2. Department of Obstetrics and Gynaecology; Helsinki University Central Hospital; Helsinki Finland
3. Department of Gynaecology and Paediatrics; Helsinki University Central Hospital; Helsinki Finland
4. Department of Gynaecology and Obstetrics; Hyvinkää Hospital; Helsinki and Uusimaa district Finland
5. THL National Institute for Health and Welfare; Helsinki Finland
6. Department of Public Health Sciences; Karolinska institute; Stockholm Sweden
7. Clinitec; Karolinska Institute/Department of Gynaecology and Obstetrics; Karolinska University Hospital; Stockholm Sweden
8. Department of Evaluation and Analysis; Epidemiology and Methodological Support Unit; National Board of Health and Welfare; Stockholm Sweden
9. Department of Obstetrics and Gynaecology; Institution of Clinical Sciences; University of Lund; Lund Sweden
10. Department of Global Public Health and Primary Care; University of Bergen; Bergen Norway
11. Medical Birth Register of Norway; Norwegian Institute of Public Health; Bergen Norway
12. Department of Obstetrics and Gynaecology; Haukeland University Hospital/University of Bergen; Bergen Norway
13. Department of Obstetrics and Gynaecology; Landspitali University Hospital; Reykjavik Iceland
14. Department of Obstetrics and Gynaecology; Holbaek University Hospital; Holbaek Denmark