1. Department of Obstetrics and Gynecology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seongnam, Korea.
3. Department of Obstetrics and Gynecology, Kyung Hee University School of Medicine, Seoul, Korea.
4. Division of Maternal and Fetal Medicine, Department of Obstetrics and Gynecology, Konkuk University Medical Center, Konkuk University School of Medicine, Seoul, Korea.
5. Department of Obstetrics and Gynecology, Graduate School of Medicine, Dongguk University, Seoul, Korea.
6. Hamchoon Women's Clinic, Seoul, Korea.
7. Department of Obstetrics and Gynecology, Seoul St. Mary's Hospital, The Catholic University of Korea College of Medicine, Seoul, Korea.
8. Department of Obstetrics and Gynecology, Kwandong University College of Medicine, Seoul, Korea.
9. Department of Obstetrics and Gynecology, Ewha Womans University School of Medicine, Seoul, Korea.
10. Department of Obstetrics and Gynecology, Korea University College of Medicine, Seoul, Korea.
11. Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.
12. Department of Obstetrics and Gynecology, Bucheon St. Mary's Hospital, The Catholic University of Korea College of Medicine, Bucheon, Korea.