1. Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea
2. Department of Obstetrics and Gynecology, Seoul National University Hospital, Seoul, Korea
3. Department of Biostatistics, Epidemiology and Informatics, Perelman School of Medicine, University of Pennsylvania, Philadelphia
4. Department of Anesthesiology and Pain Medicine, Seoul Metropolitan Government Seoul National University Boramae Medical Center, Seoul, Korea
5. Department of Anesthesiology and Pain Medicine, Seoul National University College of Medicine, Seoul, Korea
6. Institute for Biomedical Informatics, University of Pennsylvania, Philadelphia