1. Obstetrics and Gynaecology; University of Helsinki and Helsinki University Hospital; Helsinki Finland
2. Children's Hospital; University of Helsinki and Helsinki University Hospital; Helsinki Finland
3. Finnish Cancer Registry; Institute for Statistical and Epidemiological Cancer Research; Helsinki Finland
4. School of Health Sciences; University of Tampere; Tampere Finland
5. Department of Research; Cancer Registry of Norway; Oslo Norway
6. Icelandic Cancer Registry; Reykjavik Iceland
7. Faculty of Medicine; Laeknagardur, University of Iceland; Reykjavik Iceland
8. Department of Medical Epidemiology and Biostatistics; Karolinska Institutet; Stockholm Sweden