1. Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Dongguk University Ilsan Hospital, Goyang, Korea.
3. Department of Obstetrics and Gynecology, CHA Gangnam Medical Center, CHA University School of Medicine, Seoul, Korea.
4. Department of Obstetrics and Gynecology, Keimyung University School of Medicine, Daegu, Korea.