1. Department of Obstetrics and Gynecology, Hokkaido University Graduate School of Medicine
2. JCOG Data Center/Operations Office, National Cancer Center
3. Department of Obstetrics and Gynecology, Kurume University School of Medicine
4. Department of Obstetrics and Gynecology, Faculty of Medicine, University of Tsukuba
5. Department of Obstetrics and Gynecology, Kitasato University School of Medicine
6. Department of Obstetrics and Gynecology, Keio University School of Medicine
7. Department of Obstetrics and Gynecology, Tohoku University School of Medicine, Japan