1. Centre of Public Health Sciences; School of Health Sciences; University of Iceland; Reykjavik Iceland
2. Division of Health Information and Research; Directorate of Health; Reykjavik Iceland
3. Department of Medicine; Landspitali University Hospital; Reykjavík Iceland
4. Icelandic Birth Register; Department of Obstetrics and Gynecology; Landspitali University Hospital; Reykjavik Iceland