1. 1 Clinic of Obstetrics and Gynaecology, University Hospital Pleven, Department of Obstetrics and Gynaecology, Medical University – Pleven , Bulgaria
2. 2 Department of Pre-clinical and Clinical Sciences, Faculty of Pharmacy, Medical University – Pleven , Bulgaria
3. 3 Department of Clinical Laboratory, Clinical Immunology and Allergology, Medical University – Pleven , Bulgaria