1. Department of Obstetrics and Gynaecology; University of Fukui; Fukui; Japan
2. Department of Obstetrics and Gynaecology; Fujita Health University School of Medicine; Toyoake; Aichi; Japan
3. Department of Obstetrics and Gynaecology; Saiseikai Yamagata Hospital; Oki-machi; Yamagata; Japan
4. Department of Obstetrics and Gynaecology; Hokkaido University School of Medicine; Sapporo; Hokkaido; Japan