1. Department of Obstetrics and Gynecology, The Jikei University School of Medicine, Tokyo, Japan.
2. Department of Obstetrics and Gynecology, Daisan Hospital, The Jikei University School of Medicine, Tokyo, Japan.
3. Department of Obstetrics and Gynecology, Kashiwa Hospital, The Jikei University School of Medicine, Chiba, Japan.
4. Department of Obstetrics and Gynecology, Katsushika Medical Center, The Jikei University School of Medicine, Tokyo, Japan.