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