1. Department of Obstetrics and Gynecology, Soonchunhyang University Cheonan Hospital, Cheonan, Korea.
2. Department of Obstetrics and Gynecology, Research Institute of Medical Science, Konkuk University School of Medicine, Seoul, Korea.
3. Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seongnam, Korea.
4. Department of Obstetrics and Gynecology, Ajou University School of Medicine, Suwon, Korea.
5. Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.
6. Research Coordinating Center, Konkok University Medical Center, Seoul, Korea.