1. Department of Obstetrics and Gynecology Chengdu Second People's Hospital Chengdu Sichuan People's Republic of China
2. Department of Obstetrics and Gynecology Jianyang Maternal and Child Health Hospital Jianyang Sichuan People's Republic of China
3. Department of Obstetrics and Gynecology Dazhou Central Hospital Dazhou Sichuan People's Republic of China
4. Department of Obstetrics and Gynecology The People's Hospital of Kaizhou District Chongqing People's Republic of China
5. Department of Obstetrics and Gynecology Bishan Hospital Chongqing People's Republic of China
6. Department of Obstetrics and Gynecology The Second Affiliated Hospital of Chongqing Medical University Chongqing People's Republic of China