1. Department of Nursing Science , Okayama Prefectural University , Okayama , Japan
2. Department of Obstetrics , Kaba Memorial Hospital , Shizuoka , Japan
3. Department of Human Ecology , Okayama University Graduate School of Environmental and Life Science , Okayama , Japan
4. Department of Social Medicine , National Center for Child Health and Development , Tokyo , Japan
5. Department of Obstetrics and Gynecology, Maternal and Perinatal Care Center, Seirei Hamamatsu General Hospital, Shizuoka , Japan
6. Department of Epidemiology , Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences , Okayama , Japan
7. Department of Social and Behavioral Sciences , Harvard School of Public Health , Boston, MA , USA