1. Clinic of Gastroenterology, University Hospital “Alexandrovska,” Sofia, Bulgaria
2. Clinic of Obstetrics and Gynecology, Acibadem City Clinic Tokuda Hospital, Sofia, Bulgaria
3. Obstetric Clinic, University Hospital “Dr. Georgi Stranski,” Pleven, Bulgaria
4. Clinic of Oncological Surgery, University Hospital “Dr. Georgi Stranski, Pleven, Bulgaria
5. Department of General and Clinical Pathology, University Hospital “Dr. Georgi Stranski,” Pleven, Bulgaria