1. Department of Obstetrics and Gynecology, Keio University School of Medicine, Tokyo, Japan
2. Department of Obstetrics and Gynecology, Nerima General Hospital, Tokyo, Japan
3. Department of Obstetrics and Gynecology, Hino Municipal Hospital, Tokyo, Japan
4. Department of Obstetrics and Gynecology, Federation of National Public Service Personnel Mutual Aid Associations, Tachikawa Hospital, Tokyo, Japan
5. Department of Obstetrics and Gynecology, Seibo Hospital, Tokyo, Japan
6. Department of Obstetrics and Gynecology, Hiratsuka City Hospital, Hiratsuka-shi, Japan
7. Department of Obstetrics and Gynecology, Japanese Red Cross Ashikaga Hospital, Ashikaga-shi, Japan
8. Department of Obstetrics and Gynecology, Japanese Red Cross Shizuoka Hospital, Shizuoka-shi, Japan
9. Department of Obstetrics and Gynecology, Japanese Red Cross Nasu Hospital, Ootawara-shi, Japan
10. Department of Obstetrics and Gynecology, Ogikubo Hospital, Tokyo, Japan
11. Department of Obstetrics and Gynecology, National Hospital Organization Saitama Hospital, Wakou-shi, Japan
12. Department of Obstetrics and Gynecology, Tokyo Dental College Ichikawa General Hospital, Ichikawa-shi, Japan
13. Department of Obstetrics and Gynecology, Shizuoka City Shimizu Hospital, Shizuoka-shi, Japan
14. Department of Obstetrics and Gynecology, Tokyo Medical Center, Tokyo, Japan
15. Department of Obstetrics and Gynecology, Saiseikai Yokohama-shi Tobu Hospital, Yokohama-shi, Japan
16. Department of Obstetrics and Gynecology, Keiyu Hospital, Yokohama-shi, Japan
17. Department of Obstetrics and Gynecology, Tokyo Adventist Hospital, Tokyo, Japan
18. Department of Obstetrics and Gynecology, Kawasaki Municipal Kawasaki Hospital, Kawasaki, Japan