1. Department of Public Health; Section for General Medical Practice; Aarhus University; Aarhus C Denmark
2. Clinical Epidemiology; Department of Clinical Medicine; Aarhus University; Aarhus C Denmark
3. Department of Public Health; Section for Epidemiology; Aarhus University; Aarhus C Denmark
4. Department of Obstetrics and Gynaecology; Odense University Hospital; Odense Denmark
5. Department of Epidemiology; Fielding School of Public Health; University of California, Los Angeles (UCLA); Los Angeles CA USA
6. National Institute for Health and Welfare; Helsinki University; Helsinki Finland