1 Department of Perinatology and Gynecology, Kagawa University School of Medicine, 1750-1 Ikenobe, Miki, Kagawa, 761-0793, Japan. toshi28@med.kagawa-u.ac.jp.
2 Department of Perinatology and Gynecology, Kagawa University School of Medicine, 1750-1 Ikenobe, Miki, Kagawa, 761-0793, Japan.
3 GE Yokogawa Medical Systems, Nishihara 8-38-29-3, Asaminami-ku, Hiroshima, 731-0113, Japan.