1. Department of Obstetrics and Gynaecology, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland
2. Department of Obstetrics and Gynaecology, Medical Research Center Oulu, Oulu University Hospital, Oulu, Finland
3. Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Helsinki, Finland
4. School of Health Sciences, University of Tampere, Tampere, Finland