1. Departments of Obstetrics and Gynaecology Women's and Children's Division Oslo University Hospital Oslo Norway
2. Department of International Public Health Norwegian Institute of Public Health Oslo Norway
3. Faculty of Medicine University of Oslo Oslo Norway
4. Department of Obstetrics and Gynaecology Institute of Clinical Sciences Sahlgrenska Academy Gothenburg Sweden
5. Department of Genes and Environment Norwegian Institute of Public Health Oslo Norway
6. Department of Global Public Health and Primary Care University of Bergen Bergen Norway