1. Department of Gynecology, Tama-Hokubu Medical Center, Tokyo Metropolitan Health and Medical Treatment Corporation, Higashimurayama, Tokyo, Japan
2. Department of Obstetrics and Gynecology, Osaka University, Osaka, Japan
3. Department of Obstetrics and Gynecology, Yokohama City University, Yokohama, Japan
4. Department of Obstetrics and Gynecology, University of Niigata, Niigata, Japan