1. Department of Obstetrics and Gynecology, Oulu University Hospital, Oulu, Finland;
2. Child and Adolescent Health and Wellbeing Unit, National Institute for Health and Welfare, Oulu, Finland;
3. Finnish Institute for Occupational Health, Oulu, Finland;
4. Department of Epidemiology and Public Health, Faculty of Medicine, Imperial College, London, U.K.;
5. Institute of Health Sciences and Biocenter Oulu, Faculty of Medicine, University of Oulu, Oulu, Finland.