1. West China Second University Hospital, West China Women's and Children's Hospital; Department of Obstetrics and Gynecology; No. 17, Section Three, Ren Min Nan Lu Avenue Chengdu Sichuan China 610041
2. West China Hospital, Sichuan University; No. 37, Guo Xue Xiang Chengdu Sichuan China 610041
3. West China Hospital, Sichuan University; Chinese Cochrane Centre, Chinese Clinical Trial Registry, Chinese Evidence-Based Medicine Centre, INCLEN Resource and Training Centre; No. 37, Guo Xue Xiang Chengdu Sichuan China 610041