1. Center for Perinatal Medicine Tohoku University Hospital Sendai Miyagi Japan
2. Department of Obstetrics and Gynecology Ehime University Graduate School of Medicine Toon Ehime Japan
3. Division of Public Health, Hygiene and Epidemiology Tohoku Medical Pharmaceutical University Sendai Miyagi Japan
4. Department of Obstetrics and Gynecology National Hospital Organization Mie Chuo Medical Center Tsu Mie Japan
5. Department of Obstetrics and Gynecology Tohoku University Graduate School of Medicine Sendai Miyagi Japan
6. Department of Obstetrics and Gynecology Rakuwakai Otowa Hospital Kyoto Japan
7. Department of Obstetrics and Gynecology Okayama City General Medical Center Okayama Japan
8. Suzuka University of Medical Science Suzuka Mie Japan