1. Department of Obstetrics and Gynaecology; University of Ulsan College of Medicine, Ulsan University Hospital; Ulsan Korea
2. Department of Obstetrics and Gynaecology; Hallym University, Dongtan Sacred Heart Hospital; Hwaseong Korea
3. Health Promotion Centre, the Catholic University of Korea Yeouido St Mary's Hospital; Seoul Korea
4. Department of Obstetrics and Gynaecology; University of Ulsan College of Medicine, Asan Medical Centre; Seoul Korea