1. Department of Obstetrics and Gynecology 1 Kawasaki Medical School Kurashiki Japan
2. Department of Obstetrics and Gynecology Kitasato University Tokyo Japan
3. Public Interest Incorporated Foundation Japan Council for Quality Health Care Tokyo Japan
4. Department of Obstetrics and Gynecology Showa University School of Medicine Tokyo Japan
5. Department of Obstetrics and Gynecology Faculty of Medicine, Mie University Tsu Japan
6. Department of Obstetrics and Gynecology School of Medicine, Fukushima Medical University Fukushima Japan