1. Department of Obstetrics and Gynecology, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
2. Institute of Women's Life Medical Science, Yonsei University College of Medicine, Seoul, Korea.
3. Department of Obstetrics and Gynecology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.
4. Department of Obstetrics and Gynecology, Keimyung University School of Medicine, Daegu, Korea.
5. Department of Obstetrics and Gynecology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.
6. Department of Obstetrics and Gynecology, Ewha Womans University College of Medicine, Seoul, Korea.