1. Faculty of Medicine, University of Belgrade, Belgrade, Serbia
2. Department of Gynecology and Obstetrics, Faculty of Medical Sciences, University of Kragujevac, Kragujevac, Serbia
3. Institute of Epidemiology, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
4. Department of Epidemiology, Faculty of Medical Sciences, University of Kragujevac, Kragujevac, Serbia