1. Department of Women's and Children's Health, Division of Reproductive and Perinatal Health, Karolinska Institutet, Stockholm, Sweden
2. Department of Medicine, Clinical Epidemiology Unit, Karolinska University Hospital, Karolinska Institutet, Stockholm, Sweden
3. Centre for Epidemiology, National Board of Health and Welfare, Stockholm, Sweden
4. Department of Woman and Child Health, Uppsala University, Uppsala, Sweden