Shunji Suzuki1, Emi Shimizu2, Michiyo Kinoshita2, Sakae Araki2. 1. Department of Obstetrics and Gynecology, Japanese Red Cross Katsushika Maternity Hospital, 5-11-12 Tateishi, Katsushika-ku, Tokyo, 124-0012, Japan. czg83542@mopera.ne.jp. 2. Department of Obstetrics and Gynecology, Japanese Red Cross Katsushika Maternity Hospital, 5-11-12 Tateishi, Katsushika-ku, Tokyo, 124-0012, Japan.