1. Department of Obstetrics and Gynecology, Qingbaijiang District People’s Hospital, Chengdu, Sichuan, China
2. Department of Obstetrics and Gynecology, Southwest Medical University, Luzhou, Sichuan, China
3. Department of Obstetrics and Gynecology, Mianyang Central Hospital, Mianyang, Sichuan, China
4. Department of Obstetrics and Gynecology, Chengdu Medical College, Chengdu, Sichuan, China.