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 Second University Hospital, Sichuan University; Department of Obstetrics and Gynecology; No. 20, 3rd section, Renmin South Road Chengdu Sichuan China 610041
3. The University of Newcastle; Mother and Baby Center, School of Medicine and Public Health; Callaghan campus New Castle New South Wales China 2308
4. 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