1. Department of Obstetrics and Gynecology, Iwate Medical University School of Medicine, Yahaba 028-3695, Japan
2. Department of Obstetrics and Gynecology, Akita University School of Medicine, Akita 010-8543, Japan
3. Department of Obstetrics and Gynecology, Hirosaki University School of Medicine, Aomori 036-8563, Japan
4. Department of Obstetrics and Gynecology, St. Mary’s Hospital, Fukuoka 830-8543, Japan