1. West China 2nd Hospital, Sichuan University; Reproductive Medical Centre, Department of Obstetrics and Gynecology; Chengdu China 610041
2. West China Hospital, Sichuan University; Department of Geriatrics; No. 37, Guo Xue Xiang Chengdu Sichuan China 610041
3. West China Hospital, Sichuan University; Chinese Cochrane Centre; No. 37, Guo Xue Xiang Chengdu Sichuan China 610041
4. Sichuan University; Institute of Preliminary and Forensic Medicine; Chengdu China
5. San Joaquin Community Hospital; 12704 Schooner Beach Dr Bakersfield California USA
6. West China 2nd Hospital, Sichuan University; Reproductive Medicine Centre, Department of Obstetrics and Gynaecology; Chengdu Sichuan China 610041