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