1. Department of Obstetrics and Gynaecology; Blekinge Hospital; Karlskrona Sweden
2. Department of Obstetrics and Gynaecology; Clintec; Karolinska University Hospital; Stockholm Sweden
3. Department of Obstetrics and Gynaecology; University Hospital; Helsinki Finland
4. Department of Obstetrics; Rigshospitalet; Copenhagen Denmark
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 Gynaecology; Landspitali University Hospital; Reykjavik Iceland
8. Department of Gynaecology and Paediatrics; University Hospital; Helsinki Finland
9. Department of Obstetrics and Gynaecology; Haukeland University Hospital; University of Bergen; Bergen Norway
10. Department of Evaluation and Analysis, Epidemiology and Methodological support unit; National Board of Health and Welfare; Stockholm Sweden
11. Department of Public Health Sciences; Karolinska Institutet; Stockholm Sweden
12. Fertility Clinic; Rigshospitalet; Copenhagen University Hospital; Copenhagen Denmark
13. Department of Obstetrics and Gynaecology; Holbaek Hospital; Holbaek and University of Copenhagen; Copenhagen Denmark
14. THL National Institute for Health and Welfare; Helsinki Finland
15. Nordic School of Public Health; Gothenburg Sweden
16. Department of Reproduction Epidemiology; Tornblad Institute; Institution of Clinical Sciences; Lund University; Lund Sweden