1. Department of Obstetrics and Gynecology, Peking University First Hospital, Beijing, China
2. Department of Obstetrics and Gynecology, Obstetrics and Gynecology Hospital of Fudan University, Shanghai, China
3. Department of Obstetrics and Gynecology, The Third affiliated Hospital of Guangzhou Medical University, Guangzhou, China
4. Department of Obstetrics and Gynecology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
5. Department of Obstetrics and Gynecology, The Third Affiliated Hospital of Zhengzhou University, Zhengzhou, China
6. Department of Obstetrics and Gynecology, Nanjing maternity and Child Health Care Hospital, Nanjing, China
7. Department of Obstetrics and Gynecology, Obstetrics and Gynecology Hospital of Urumqi Municipality, Urumqi Municipality, China
8. Department of Obstetrics and Gynecology, The Affiliated Hospital of Inner Mongolia Medical University, Hohhot, China
9. Department of Obstetrics and Gynecology, The Maternal and Child Health Hospital of the Guangxi Zhuang Autonomous Region, Nanning, China
10. Department of Obstetrics and Gynecology, Gansu Province Hospital, Lanzhou, China
11. Department of Obstetrics and Gynecology, The Second Hospital of Hebei Medical University, Shijiazhuang, China