1. Department of Obstetrics and Gynecology, CHA Gangnam Medical Center, CHA University, Seoul, Korea
2. Department of Obstetrics and Gynecology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
3. Department of Obstetrics and Gynecology, The Catholic University, Seoul, Korea
4. Department of Obstetrics and Gynecology, Sungkyunkwan University, Seoul, Korea
5. Department of Obstetrics and Gynecology, Seoul National University, Seoul, Korea
6. Department of Obstetrics and Gynecology, Ajou University, Suwon, Korea
7. Department of Obstetrics and Gynecology, Chung-Ang University Hospital, Chung-Ang University School of Medicine, Seoul, Korea