1. Department of Obstetrics and Gynecology, Gachon University Gil Medical Center, Gachon University College of Medicine, Incheon, Korea.
2. Department of Obstetrics and Gynecology, Ewha Womans University Mokdong Hospital, Ewha Womans University College of Medicine, Seoul, Korea.
3. Department of Obstetrics and Gynecology, Kyung-Hee University Hospital at Gangdong, Kyung Hee University School of Medicine, Seoul, Korea.