1. Department of Obstetrics and Gynecology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Jeju National University College of Medicine, Jeju National University Hospital, Jeju, Korea.
3. Department of Obstetrics and Gynecology, Eulji University, Nowon Eulji Medical Center, Seoul, Korea.