1. Department of Obstetrics and Gynecology Nanfang Hospital, Southern Medical University Guangzhou China
2. Department of Obstetrics and Gynecology The Affiliated Hospital of Qingdao University Qingdao China
3. Department of Gynecology The Forth Hospital of Hebei Medical University Shijiazhuang China
4. Department of Obstetrics and Gynecology The First Affiliated Hospital of Zhengzhou University Zhengzhou China
5. Department of Obstetrics and Gynecology Guizhou People's Hospital Guiyang China
6. Department of Obstetrics and Gynecology Xijing Hospital of Airforce Medical University Xi'an China
7. Department of Obstetrics and Gynecology Affiliated Jiangmen Hospital of SUN YAT‐SEN University Jiangmen China