Xinming Li1, Hua Pan2, Qian Sun3. 1. Department of Gynecology, People's Hospital of Rizhao, Rizhao, China. 2. Department of Gynecology Clinic, People's Hospital of Rizhao, Rizhao, China. 3. Department of Obstetrics, People's Hospital of Rizhao, Rizhao, China - qinjianguo4808@163.com.