1. Department of Obstetrics and Gynecology; West China Second University Hospital, West China Women's and Children's Hospital; Chengdu China
2. Department of Obstetrics and Gynecology; West China Second University Hospital, Sichuan University; Chengdu China
3. Cochrane China; West China Hospital, Sichuan University; Chengdu China
4. Department of Obstetrics and Gynecology; People's Hospital of Deyang City; Deyang China
5. Department of Obstetrics and Gynecology; Chengdu Women & Children Central Hospital; Chengdu China