1. Department of Obstetrics and Gynecology , Medical University – Pleven , Bulgaria
2. Department of Oncogynaecology , Georgi Starnski University Hospital , Pleven , Bulgaria
3. Department of Obstetrics and Gynecology , Multiprofile Hospital for Active Treatment “St. Sofia” , Sofia , Bulgaria
4. Department of Clinical Laboratory, Clinical Immunology and Allergology , Medical University – Pleven , Bulgaria
5. Department of Surgical Propaedeutics , Medical University – Pleven , Bulgaria