1. Department of Obstetrics and Gynecology, Soonchunhyang Seoul Hospital, Soonchunhyang University College of Medicine, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Soonchunhyang Bucheon Hospital, Soonchunhyang University College of Medicine, Bucheon, Korea.
3. Department of Obstetrics and Gynecology, Soonchunhyang Cheonan Hospital, Soonchunhyang University College of Medicine, Cheonan, Korea.