1. Department of Obstetrics and Gynecology, KonKuk University Medical Center, Konkuk University School of Medicine, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea.
3. Department of Obstetrics and Gynecology, CHA Gangnam Medical Center, CHA University, Seoul, Korea.
4. Department of Obstetrics and Gynecology, Gangseo Mizmedi Hospital, Seoul, Korea.
5. Department of Obstetrics and Gynecology, CHA Bundang Medical Center, CHA University, Seongnam, Korea.
6. Department of Obstetrics and Gynecology, National Medical Center, Seoul, Korea.