1. Department of Obstetrics and Gynecology, CHA Bundang Medical Center CHA University School of Medicine, Seongnam, Korea
2. Department of Biomedical Systems Informatics, Division of Biostatistics, Yonsei University College of Medicine, Seoul, Korea
3. Department of Obstetrics and Gynecology, CHA Gangnam Medical Center CHA University School of Medicine, Seoul, Korea