1. Department of Women's and Children's Health, Division of Obstetrics and Gynecology, Karolinska Institutet and Karolinska University Hospital, Stockholm, Sweden
2. Department of Clinical Sciences at Danderyd Hospital, Karolinska Institutet, Stockholm, Sweden
3. Department of Obstetrics and Gynecology, Danderyd Hospital, Stockholm, Sweden
4. Statisticon AB, Uppsala, Sweden