1. Tohoku University School of Medicine Department of Obstetrics and Gynecology, , Sendai , Japan
2. Hokkaido University School of Medicine Department of Obstetrics and Gynecology, , Sapporo , Japan
3. Kobe University Graduate School of Medicine Department of Obstetrics and Gynecology, , Kobe , Japan
4. Kyorin University Faculty of Medicine Department of Obstetrics and Gynecology, , Mitaka , Japan
5. Iwate Medical University Department of Obstetrics and Gynecology, , Shiwa , Japan
6. Yamagata University Faculty of Medicine Department of Obstetrics and Gynecology, , Yamagata , Japan