1. Department of Obstetrics and Gynaecology, Sundsvall Hospital, Sundsvall, Sweden, , Department of Obstetrics and Gynaecology, Umeå University Hospital, Umeå, Sweden
2. Department of Obstetrics and Gynaecology, Umeå University Hospital, Umeå, Sweden
3. Department of Public Health and Clinical Medicine, Umeå University, Umeå, Sweden