1. Faculty of Medicine, University of Belgrade, 11000 Belgrade, Serbia
2. Department of Gynecology and Obstetrics, Faculty of Medical Sciences, University of Kragujevac, 34000 Kragujevac, Serbia
3. Institute of Epidemiology, Faculty of Medicine, University of Belgrade, 11000 Belgrade, Serbia
4. Department of Epidemiology, Faculty of Medical Sciences, University of Kragujevac, 34000 Kragujevac, Serbia