1. Department of Perinatology and Gynecology , Kagawa University School of Medicine , Miki , Kagawa , Japan
2. Department of Obstetrics and Gynecology , Miyake Clinic , Okayama , Okayama , Japan
3. Department of Obstetrics and Gynecology, Miyake Clinic , Okayama , Okayama , Japan
4. Department of Perinatology and Gynecology , Kagawa University Graduate School of Medicine , Kagawa , Japan