1. Department of Obstetrics and Gynecology, Sichuan University West China Second University Hospital, Chengdu, China;
2. Key Laboratory of Birth Defects and Related Diseases of Women and Children (Sichuan University), Ministry of Education, Chengdu, China;
3. West China School of Medicine, Sichuan University, Chengdu, China;
4. Department of Physiology, West China School of Preclinical and Forensic Medicine, Sichuan University, Chengdu, China;
5. Center for Evidence-Based Medicine and Clinical Research, Taihe Hospital, Hubei University of Medicine, Shiyan, China;
6. Department of Evidence based Medicine and Clinical Epidemiology, West China Hospital, Sichuan University, Chengdu, China