1. Department of Obstetrics and Gynecology; West China Second University Hospital, Sichuan University, Key Laboratory of Birth Defects and Related Diseases of Women and Children (Sichuan University), Ministry of Education; Chengdu China
2. Department of Obstetrics and Gynecology; Maternity and Child Care Service Centers in Fujian Province; Fuzhou China
3. Department of Obstetrics and Gynecology; First Affiliated Hospital of Chongqing Medical University; Chongqing China
4. Department of Obstetrics and Gynecology, Beijing Obstetrics and Gynecology Hospital; Capital Medical University; Beijing China
5. Department of Obstetrics and Gynecology, Beijing Friendship Hospital; Capital Medical University; Beijing China
6. Department of Obstetrics and Gynecology; Obstetrics and Gynecology Hospital of Fudan University; Shanghai China
7. Department of Obstetrics and Gynecology; Sichuan Provincial People's Hospital; Chengdu China
8. Department of Obstetrics and Gynecology; Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University; Guangzhou China
9. Department of Obstetrics and Gynecology; Daping Hospital of the Third Military Medical University; Chongqing China