1. Department of Obstetrics and Gynecology, Korea 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, Konkuk University School of Medicine, Seoul, Korea.
4. Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Yonsei University College of Medicine, Yonsei University Health System, Seoul, Korea.