1. Department of Obstetrics and Gynecology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
2. Departments of Obstetrics and Gynecology, Osaka University Graduate School of Medicine, Suita, Japan
3. Department of Obstetrics and Gynecology, Yokohama City University School of Medicine, Yokohama, Japan
4. Department of Preventive Medicine, Faculty of Medicine, Saga University, Saga, Japan
5. Department of Obstetrics and Gynecology, Hokkaido University Graduate School of Medicine, Sapporo, Japan