1. Department of Obstetrics Gynecology Nippon Medical School Hospital Tokyo Japan
2. Japanese Organization of Prevention of Preterm Delivery (JOPP) Tokyo Japan
3. Department of Obstetrics Gynecology International University of Health and Welfare Narita Hospital Chiba Japan
4. Department of Obstetrics Gynecology Toyama University Hospital Toyama Japan
5. You Women's Clinic Kanagawa Japan
6. Toho Women's Clinic Tokyo Japan
7. Department of Obstetrics Gynecology Nippon Medical School Tamanagayama Hospital Tokyo Japan
8. Department of Obstetrics Gynecology Showa University Koto Toyosu Hospital Tokyo Japan