1. Department of Obstetrics and Gynecology, Ajou University School of Medicine, Suwon, Korea.
2. Department of Obstetrics and Gynecology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
3. Department of Obstetrics and Gynecology, Korea University College of Medicine, Seoul, Korea.
4. Department of Obstetrics and Gynecology, Ewha Womans University School of Medicine, Seoul, Korea.
5. Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea.
6. Department of Obstetrics and Gynecology, Yonsei University College of Medicine, Seoul, Korea.