1. Japanese Organization of Prevention of Preterm Delivery; Tokyo Japan
2. Department of Obstetrics and Gynecology; Showa University Koto Toyosu Hospital; Tokyo Japan
3. Department of Obstetrics and Gynecology; Nippon Medical School, Tama-Nagayama Hospital; Tokyo Japan
4. Department of Obstetrics and Gynecology; International University of Health and Welfare; Tochigi Japan
5. Fetal Medicine Research Unit; Kanagawa Japan
6. Department of Obstetrics and Gynecology; Nippon Medical School, Musashi-Kosugi Hospital; Tokyo Japan
7. Department of Obstetrics and Gynecology; Tokyo Women's Medical University; Tokyo Japan
8. Department of Obstetrics and Gynecology; Tokyo University; Tokyo Japan
9. Department of Obstetrics and Gynecology; Kyorin University; Tokyo Japan
10. Department of Obstetrics and Gynecology; Showa University School of Medicine; Tokyo Japan