1. Department of Epidemiology and Disaster Medicine, Faculty of Public Health, Medical University of Plovdiv, 4000 Plovdiv, Bulgaria
2. Department of Social Medicine and Public Health, Faculty of Public Health, Medical University of Plovdiv, 4000 Plovdiv, Bulgaria
3. Department of Obstetrics and Gynecology, Neonatology Unit, Faculty of Medicine, Medical University of Plovdiv, 4000 Plovdiv, Bulgaria