1. Department of Obstetrics and Gynecology, Yonsei University College of Medicine, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
3. Department of Obstetrics and Gynecology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.
4. Department of Obstetrics and Gynecology, Research Institute of Medical Science, Konkuk University School of Medicine, Seoul, Korea.
5. Department of Obstetrics and Gynecology, Seoul National University Hospital, Seoul, Korea.
6. Department of Obstetrics and Gynecology, Ajou University School of Medicine, Suwon, Korea.
7. Department of Obstetrics and Gynecology, Eulji Medical Center, Eulji University School of Medicine, Daejeon, Korea.
8. Department of Obstetrics and Gynecology, Guro Hospital, Korea University College of Medicine, Seoul, Korea.
9. Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seongnam, Korea.