1. Department of Gynecology, Xuzhou Maternity and Child Health Care Hospital, Xuzhou Medical University, Xuzhou, Jiangsu 221009, P.R. China
2. Cervical Disease Center, Xuzhou Maternity and Child Health Care Hospital, Xuzhou Medical University, Xuzhou, Jiangsu 221009, P.R. China
3. Department of Gynaecology and Obstetrics, The Affiliated Hospital of Xuzhou Medical University, Xuzhou, Jiangsu 221009, P.R. China
4. B Ultrasonic Room, Xuzhou Maternity and Child Health Care Hospital, Xuzhou Medical University, Xuzhou, Jiangsu 221009, P.R. China