1. The OCEAN Study Group (The Obstetrical Gynecological Society of Osaka), Kawaramachi, Chuo-ku, Osaka, Japan
2. Department of Obstetrics and Gynecology, Osaka University Graduate School of Medicine, Yamadaoka, Suita, Osaka, Japan
3. Department of Obstetrics and Gynecology, Osaka Medical College Graduate School of Medical Sciences, Takatsuki, Osaka, Japan
4. Department of Obstetrics and Gynecology, Osaka City University Graduate School and Faculty of Medicine, Abeno-ku, Osaka, Japan
5. Department of Obstetrics and Gynecology, Kansai Medical University Graduate School of Medicine, Hirakata, Osaka, Japan
6. Department of Obstetrics and Gynecology, Kinki University Graduate School of Medical Sciences, Osaka-Sayama, Osaka, Japan
7. Department of Pathology, Osaka University Graduate School of Medicine, Yamadaoka, Suita, Osaka, Japan
8. Center for Cancer Control and Statistics, Osaka Medical Center for Cancer and Cardiovascular Diseases, Higashinari-ku, Osaka, Japan
9. Department of Obstetrics and Gynecology, Yokohama City University Graduate School of Medicine, Kanazawa-ku, Yokohama, Kanagawa, Japan
10. Department of Obstetrics and Gynecology, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Japan