1. The Department of Obstetrics and Gynecology, Sanggye Paik Hospital, School of Medicine, Inje University, Seoul, Republic of Korea.
2. The Department of Anesthesiology and Pain Medicine, Gyeongsang National University Changwon Hospital, School of Medicine, Gyeongsang National University, Changwon, Gyeongnam, Republic of Korea.
3. The Department of Obstetrics and Gynecology, Ewha Womans University Seoul Hospital, College of Medicine, Ewha Womans University, Seoul, Republic of Korea.