1. Department of Medical Education, Yokohama City University School of Medicine, Yokohama, Japan.
2. Medley, Inc., Tokyo, Japan.
3. The Medical Corporations of Tsuzuki-kai Tsuzuki Ladies' Clinic, Yokohama, Japan.
4. The Medical Corporations of Ikuju-kai Isogo You Ladies' Clinic, Yokohama, Japan.
5. Department of Biostatistics, Yokohama City University School of Medicine, Yokohama, Japan.
6. Department of Obstetrics and Gynecology, Yokohama City University School of Medicine, Yokohama, Japan.