1. Department of Obstetrics and Gynecology Yokohama City University School of Medicine Yokohama Japan
2. Center for Health Service Sciences Yokohama National University Yokohama Japan
3. Department of Obstetrics and Gynecology Osaka University Graduate School of Medicine Osaka Japan
4. Department of Obstetrics and Gynecology Niigata University Graduate School of Medical and Dental Sciences Niigata Japan