1. Department of Obstetrics and Gynecology Hokkaido University Graduate School of Medicine Sapporo Japan
2. Department of Obstetrics and Gynecology Yokohama City University Graduate School of Medicine Yokohama Japan
3. Department of Public Health Dokkyo Medical University, School of Medicine Tochigi Japan
4. Perinatal Center for Maternity and Neonates Yokohama City University Medical Center Yokohama Japan
5. Obstetrics and Gynecology Mie University Graduate School of Medicine Tsu Japan
6. Department of Obstetrics and Gynecology Osaka University Graduate School of Medicine Osaka Japan
7. Department of Obstetrics and Gynecology Kobe University Graduate School of Medicine Kobe Japan