1. Department of Obstetrics and Gynecology Toho University Faculty Medicine Tokyo Japan
2. Perinatal Research Network in Japan Osaka Japan
3. The Japan Maternal Death Exploratory Committee Tokyo Japan
4. Department of Obstetrics and Gynecology St. Marianna University School of Medicine Kanagawa Japan
5. Department of Obstetrics and Gynecology Mie University School of Medicine Mie Japan
6. Division of Perinatology Maternal and Perinatal Care Center, Seirei Hamamatsu General Hospital Hamamatsu Japan
7. Department of Maternal and Fetal Medicine Osaka Medical Center and Research Institute for Maternal and Child Health Osaka Japan
8. Department of Obstetrics and Gynecology Showa University School of Medicine Tokyo Japan
9. Ishiwata Obstetrics and Gynecology Hospital Ibaraki Japan