1. West China Second University Hospital, West China Women's and Children's Hospital; Department of Obstetrics and Gynecology; 2 Jiangtianlu Chengdu Sichuan China 610041
2. West China Second University Hospital, Sichuan University; Department of Obstetrics and Gynecology; Chengdu Sichuan China
3. Ministry of Education; Key Laboratory of Birth Defects and Related Diseases of Women and Children, Sichuan University; Chengdu China
4. The Second Affiliated Hospital of Chongqing Medical University; The Obstetrics and Gynecology Department; 76 Linjiang Rd Chongqing China 400010
5. The Second Affiliated Hospital of Chongqing Medical University; Center for Reproductive Medicine, Department of Obstetrics and Gynecology; 74 Linjiang Road Chongqing Chongqing China 400010
6. West China Hospital, Sichuan University; Chinese Clinical Trial Registry, Chinese Ethics Committee of Registering Clinical Trials; No. 37, Guo Xue Xiang Chengdu Sichuan China 610041
7. The Evidence-Based Medicine Consultancy Ltd; 3rd Floor Northgate House Upper Borough Walls Bath UK BA1 1RG