1. Department of Obstetrics and Gynecology, Chungnam National University Hospital, Daejeon, Korea
2. Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seongnam, Korea
3. Department of Radiology, CHA Bundang Medical Center, CHA University, Seongnam, Korea
4. Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea