1. Department of Obstetrics and Gynecology, National Medical Center, Seoul, Republic of Korea.
2. Department of Obstetrics and Gynecology, Hanyang University Hospital, Hanyang University School of Medicine, Seoul, Republic of Korea.
3. Department of Anesthesiology and Pain Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea.
4. Department of Obstetrics and Gynecology, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea.