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