doi: 10.1111/1471-0528.16754. Online ahead of print. 1 Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden. 2 Department of Obstetrics and Gynaecology, Karolinska University Hospital, Stockholm, Sweden. 3 Department of Sexual, Reproductive and Perinatal health, Dalarna University, Falun, Sweden. 4 Statisticon Inc, Uppsala, Sweden.