1. Department of Obstetrics and Gynecology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences , Okayama , Japan
2. Department of Obstetrics and Gynecology, City Hiroshima Citizens Hospital , Hiroshima , Japan
3. Department of Obstetrics and Gynecology, National Organization Fukuyama Medical Center , Hiroshima , Japan
4. Department of Obstetrics and Gynecology, Fukuyama City Hospital , Hiroshima , Japan
5. Department of Obstetrics and Gynecology, Yamaguchi University Graduate School of Medicine , Yamaguchi , Japan
6. Department of Perinatology and Gynecology, Kagawa University Graduate School of Medicine , Kagawa , Japan
7. Department of Obstetrics and Gynecology, National Hospital Organization KURE Medical Center and Chugoku Cancer Center , Hiroshima , Japan
8. Department of Obstetrics and Gynecology, Saiseikai General Hospital , Okayama , Japan
9. Department of Obstetrics and Gynecology, Prefectural Hospital , Hiroshima , Japan
10. Department of Obstetrics and Gynecology, Kagawa Prefectural Central Hospital , Kagawa , Japan
11. Department of Obstetrics and Gynecology, National Hospital Organization Iwakuni Clinical Center , Yamaguchi , Japan
12. Department of Obstetrics and Gynecology, Onomichi General Hospital , Hiroshima , Japan
13. Department of Obstetrics and Gynecology, Japanese Red Cross Matsuyama Hospital , Ehime , Japan
14. Department of Obstetrics and Gynecology, Higashi Hiroshima Medical Center , Hiroshima , Japan
15. Department of Obstetrics and Gynecology, Kagawa Rosai Hospital , Kagawa , Japan