1. a Department of Children, Young People and Families and Public Health, National Institute for Health and Welfare (THL) , University of Helsinki , Helsinki , Finland
2. b Infectious Diseases and Drug Abuse Prevention Department , National Institute for Health Development , Tallinn , Estonia
3. c Department of Hygiene & Epidemology , University of Porto Medical School , Porto , Portugal
4. d University of Zielona Góra , Zielona Góra , Poland
5. e Service System Department , National Institute for Health & Welfare , Helsinki , Finland
6. f International Centre for Reproductive Health , Ghent University , Ghent , Belgium