1. Department of Obstetrics and Gynecology, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong 510515, P.R. China
2. Department of Gynecology, Fourth Hospital, Hebei Medical University, Shijiazhuang, Hebei 050000, P.R. China
3. Department of Gynecology, Qingdao Municipal Hospital, Qingdao, Shandong 266000, P.R. China
4. Department of Obstetrics and Gynecology, The Second Hospital of Shanxi Medical University, Taiyuan, Shanxi 030000, P.R. China
5. Department of Obstetrics and Gynecology, The Second Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450000, P.R. China
6. Department of Obstetrics and Gynecology, China‑Japan Friendship Hospital, Beijing 100000, P.R. China
7. Department of Gynecology, The Affiliated Hospital of Qingdao University Medical College, Qingdao, Shandong 266000, P.R. China