1. Department of Obstetrics and Gynecology, People's Hospital of Ningxia Hui Autonomous Region, Yinchuan, Ningxia, China.
2. Department of Gynecology, General Hospital of Ningxia Medical University, Yinchuan, Ningxia, China.
3. Department of Clinical Medicine, Ningxia Medical University, Yinchuan, Ningxia, China.