1. Department of Obstetrics and Gynecology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seongnam, Korea.
3. Department of Obstetrics and Gynecology, Ajou University School of Medicine, Suwon, Korea.
4. Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.