1. Department of Obstetrics and Gynecology, Konkuk University School of Medicine, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Kangdong Sacred Heart Hospital, Hallym University College of Medicine, Seoul, Korea.
3. Department of Obstetrics and Gynecology, CHA Ilsan Medical Center, CHA University, Goyang, Korea.
4. Department of Obstetrics and Gynecology, Ewha Womans University Mokdong Hospital, Ewha Womans University College of Medicine, Seoul, Korea.