1 Department of Obstetrics and Gynecology, Yamaguchi University Graduate School of Medicine, Minami Kogushi 1-1-1, 755-8505, Ube, Japan.
2 Department of Obstetrics and Gynecology, Yamaguchi University Graduate School of Medicine, Minami Kogushi 1-1-1, 755-8505, Ube, Japan. sugino@yamaguchi-u.ac.jp.