[1] Hokkaido Univ, Dept Publ Hlth Sci, Grad Sch Med, Kita Ku, North 15,West 7, Sapporo, Hokkaido 0600838, Japan
[2] Hokkaido Univ, Ctr Environm & Hlth Sci, Kita Ku, North 12,West 7, Sapporo, Hokkaido 0600812, Japan
[3] Chuo Univ, Ctr Hlth, Shinjuku Ku, 42-8 Ichigaya Hommura Cho, Tokyo 1628473, Japan
[4] Hokkaido Univ, Dept Resp Med, Grad Sch Med, Kita Ku, North 15,West 7, Sapporo, Hokkaido 0600838, Japan
[5] Hokkaido Univ, Dept Obstet & Gynecol, Grad Sch Med, Kita Ku, North 15,West 7, Sapporo, Hokkaido 0600838, Japan
[6] Sapporo Med Univ, Sch Med, Dept Obstet & Gynecol, Chuo Ku, South 1,West 17, Sapporo, Hokkaido 0608556, Japan
[7] Asahikawa Med Univ, Sch Med, Dept Obstet & Gynecol, Midorigaoka Higashi 2-1-1-1, Asahikawa, Hokkaido 0788510, Japan