1. Department of Obstetrics and Gynecology, Cheil General Hospital and Women's Healthcare Center, Kwandong University College of Medicine, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
3. Department of Obstetrics and Gynecology, Graduate School of Medicine, Kyungpook National University, Daegu, Korea.
4. Department of Obstetrics and Gynecology, Korea University Anam Hospital, Korea University College of Medicine, Seoul, Korea.
5. Department of Obstetrics and Gynecology, Hanyang University Seoul Hospital, Hanyang University College of Medicine, Seoul, Korea.