1. Department of Obstetrics and Gynecology Peking University Third Hospital Beijing China
2. National Clinical Research Center for Obstetrics and Gynecology Beijing China
3. National Center for Healthcare Quality Management in Obstetrics Beijing China
4. Department of Obstetrics and Gynecology Maternal and Child Health Hospital of Qinhuangdao Qinhuangdao China
5. Department of Obstetrics Maternal and Child Health Hospital of Hunan Changsha China
6. Department of Obstetrics Maternal and Child Health Hospital of Guangxi Zhuang Autonomous Region Nanning China
7. Department of Obstetrics Tongzhou Maternal and Child Health Hospital of Beijing Beijing China
8. Department of Obstetrics and Gynecology The First Affiliated Hospital of Xiamen University Xiamen China
9. Maternal and Child Health Hospital of Dongchangfu District Liaocheng China
10. Department of Obstetrics Gansu Maternal and Child Health Hospital Lan Zhou China
11. Department of Obstetrics and Gynecology Changchun Obstetrics–Gynecology Hospital Changchun China
12. Fujian Maternity and Child Health Hospital Affiliated Hospital of Fujian Medical University Fu Zhou China
13. Department of Function Maternal and Child Health Hospital of Shijiazhuang Shijiazhuang China
14. Department of Obstetrics Shanxi Maternal and Child Health Hospital Taiyuan China
15. Department of Obstetrics The First Affiliated Hospital of Chongqing Medical University Chongqing China
16. Department of Obstetrics Zhengzhou Central Hospital Zhengzhou China
17. Department of Obstetrics Maternal and Child Health Hospital of Changzhi Changzhi China
18. Department of Obstetrics Maternity and Infant Hospital of Shenyang Shenyang China
19. Department of Obstetrics Hubei Maternal and Child Health Hospital Wu Han China
20. Department of Obstetrics Inner Mongolia Maternal and Child Health Hospital Hohhot China
21. Shengjing Hospital Affiliated to China Medical University Shenyang China
22. Department of Prenatal Diagnosis The Third Affiliated Hospital of Guangzhou Medical University Guangzhou China