1. Department of Obstetrics and Gynecology, Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
2. Department of Gynecology, Otaru General Hospital, Otaru, Japan.
3. Department of Anatomy II, Sapporo Medical University, Sapporo, Japan.
4. Division of Internal Medicine, Jikou-kai Clinic of Home Visits, Sapporo, Japan.