1. Department of Obstetrics and Gynecology, The Affiliated Clinical College Shenzhen Second People’s Hospital, Anhui Medical University, Hefei, P. R. China
2. Department of Ultrasound, The Second People’s Hospital of Shenzhen, Shenzhen, P. R. China
3. Department of Radiology, The Second People’s Hospital of Shenzhen, Shenzhen, P. R. China
4. Department of Obstetrics and Gynecology, The First Affiliated Hospital of Anhui Medical University, Hefei, P. R. China