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