1. Department of Obstetrics and Gynecology, College of Medicine, The Catholic University of Korea, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Ewha Womans University College of Medicine, Seoul, Korea.
3. Department of Obstetrics and Gynecology, Korea University College of Medicine, Seoul, Korea.
4. Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.
5. Department of Obstetrics and Gynecology, Samsung Medical Center, Sungkyunkwan University College of Medicine, Seoul, Korea.
6. Department of Obstetrics and Gynecology, Chung-Ang University School of Medicine, Seoul, Korea.
7. Department of Obstetrics and Gynecology, Chonnam National University Medical School, Gwangju, Korea.