1. Department of Obstetrics and Gynecology Hokkaido University Graduate School of Medicine Sapporo Japan
2. Center for Environmental and Health Sciences Hokkaido University Sapporo Japan
3. Center for Perinatal Medicine Hokkaido University Hospital Sapporo Japan
4. Faculty of Nursing Japanese Red Cross Hokkaido College of Nursing Kitami Japan
5. Department of Social Medicine Asahikawa Medical University Asahikawa Japan