1. West China Second University Hospital, Sichuan University; Department of Obstetrics and Gynecology; No. 20, Section Three, Ren Min Nan Lu Avenue Chengdu Sichuan China 610041
2. Ministry of Education; Key Laboratory of Birth Defects and Related Diseases of Women and Children (Sichuan University); Chengdu China
3. Chengdu Women and Children Central Hospital; Department of Obstetrics and Gynecology; No.1617, Ri Yue Street Chengdu Sichuan China 610091
4. West China Hospital, Sichuan University; Chinese Cochrane Centre; No. 37, Guo Xue Xiang Chengdu Sichuan China 610041
5. Emory University School of Medicine; Department of Gynecology and Obstetrics; 1639 Pierce Drive Atlanta USA WMB 4303 Atlanta