1. Department of Obstetrics and Gynecology; Hokkaido University Graduate School of Medicine; Sapporo Japan
2. Women's Health Educational System; Hokkaido University Graduate School of Medicine; Sapporo Japan
3. Department of Obstetrics and Gynecology; Kobe University Graduate School of Medicine; 7-5-1 Kusunoki-cho, Chuo-ku 650-0017 Kobe Japan
4. Department of Medicine II; Hokkaido University Graduate School of Medicine; Sapporo Japan