1. Department of Obstetrics and Gynecology, Juntendo University Faculty of Medicine, Tokyo, Japan
2. Department of Obstetrics and Gynecology, Keiai Hospital, Saitama, Japan
3. Department of Obstetrics and Gynecology, Juntendo University Urayasu Hospital, Urayasu City, Chiba, Japan
4. Aiiku Research Institute for Maternal, Child Health and Welfare, Tokyo, Japan