Affiliation: | 1. Department of Ultrasound, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, China;2. Department of Obstetrics, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, China;3. Department of Radiology, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, China;4. Department of Ultrasound, the General Hospital of the People's Liberation Army, Beijing, China |