1. Department of Obstetrics and Gynecology, College of Medicine, University of Ulsan, Ulsan University Hospital, Ulsan, Korea.
2. Department of Anesthesiology and Pain Medicine, College of Medicine, Catholic University of Korea, Seoul, Korea.
3. Department of Obstetrics and Gynecology, College of Medicine, University of Kwandong, Cheil General Hospital and Women's Healthcare Center, Seoul, Korea.