1 Department of Obstetrics and Gynecology, School of Medicine, University of Occupational and Environmental Health, Yahatanishi-ku, Kitakyushu 807-8555, Japan.
2 Department of Obstetrics and Gynecology, School of Medicine, University of Occupational and Environmental Health, Yahatanishi-ku, Kitakyushu 807-8555, Japan. Electronic address: k-yoshino@med.uoeh-u.ac.jp.