1. Department of UltrasoundBeijing Obstetrics and Gynecology Hospital, Capital Medical University Beijing China
2. Department of ObstetricsBeijing Obstetrics and Gynecology Hospital, Capital Medical University Beijing China
3. Department of RadiologyBeijing Obstetrics and Gynecology Hospital, Capital Medical University Beijing China
4. Department of Ultrasoundthe General Hospital of the People's Liberation Army Beijing China