1. Department of Gynecology and Obstetrics, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
2. Institute of Infectious Diseases, 5th Medical Center of Chinese PLA General Hospital, Beijing 100141, P.R. China
3. College of Medicine, Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China