1. Department of Obstetrics and Gynecology, Peking Union Medical College Hospital, Peking Union Medical College Chinese Academy of Medical Sciences, National Clinical Research Center for Obstetric & Gynecologic Diseases Beijing China
2. Department of Epidemiology and Biostatistics, Institute of Basic Medical Sciences Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College Beijing China
3. Department of Obstetrics and Gynecology Dalian Municipal Women and Children’s Medical Center (Group) Dalian Liaoning China
4. Department of Obstetrics and Gynecology The Fourth Hospital of Shijiazhuang Shijiazhuang Hebei China
5. Department of Obstetrics and Gynecology Hunan Maternal and Child Health Hospital Changsha Hunan China
6. Department of Obstetrics and Gynecology Huaian Maternal and Child Health Hospital Huaian Jiangsu China
7. Department of Obstetrics and Gynecology Shenzhen Maternity and Child Healthcare Hospital Shenzhen Guangdong China
8. Department of Obstetrics and Gynecology Maternal and Child Health Care Hospital of Qinhuangdao Qinhuangdao Liaoning China
9. Department of Obstetrics and Gynecology Women and Children's Health Care Hospital of Luohu Shenzhen Guangdong China
10. Department of Obstetrics and Gynecology The Second Affiliated Hospital of Soochow University Suzhou Jiangsu China
11. Department of Obstetrics and Gynecology, Changjianglu Pelvic Floor Repair Center Dalian Maternity and Child Healthcare Center (Group) Dalian Liaoning China
12. Department of Obstetrics and Gynecology Liuzhou Maternity and Child Healthcare Hospital Liuzhou Guangxi China
13. Department of Obstetrics and Gynecology Qingdao Municipal Hospital Qingdao Shandong China
14. Department of Obstetrics and Gynecology Changsha Hospital for Maternal and Child Health Care Affiliated to Hunan Normal University Changsha Hunan China