1. Ozawa Women's General Clinic Sendai Miyagi Japan
2. Department of Obstetrics and Gynecology, Faculty of Medical Sciences University of Fukui Fukui Fukui Japan
3. Sapporo Women's JR‐Tower Clinic Sapporo Hokkaido Japan
4. Tanaka Women's Clinic Saga Saga Japan
5. Division of Public Health, Hygiene and Epidemiology, Faculty of Medicine Tohoku Medical and Pharmaceutical University Sendai Miyagi Japan
6. Japan Association of Obstetricians and Gynecologists Tokyo Japan