1. Department of Obstetrics and Gynecology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan
2. Department of Obstetrics and Gynecology, Saitama Medical Center, Saitama Medical University, Saitama 350-8550, Japan
3. Department of Obstetrics and Gynecology, Juntendo University, Tokyo 113-8421, Japan