1. Department of Obstetrics and Gynecology, Nanchong Central Hospital, The Second Clinical Medical College, North Sichuan Medical University, Nanchong, PR China
2. State Key Laboratory of Ultrasound in Medicine and Engineering, College of Biomedical Engineering, Chongqing Medical University, Chongqing, PR China
3. School of Public Health and Management, Chongqing Medical University, Chongqing, PR China