1. Department of Obstetrics and Gynecology, CHA Gangnam Medical Center, CHA University, Seoul, Korea.
2. Department of Obstetrics and Gynecology, St. Vincent's Hospital, Catholic University College of Medicine, Suwon, Korea.
3. Department of Obstetrics and Gynecology, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Korea.
4. Department of Obstetrics and Gynecology, CHA Ilsan Medical Center, CHA University, Goyang, Korea.
5. Department of Obstetrics and Gynecology, Hosan Women's Hospital, Seoul, Korea.