1. Graduate School of Health Sciences, Gunma University; Maebashi Japan
2. Department of Obstetrics and Gynecology; Japan Community Health Care Organization, Gunma Chuo Hospital; Maebashi Japan
3. Department of Obstetrics and Gynecology; Japanese Red Cross Maebashi Hospital; Maebashi Japan
4. Department of Obstetrics and Gynecology; Gunma University Graduate School of Medicine; Maebashi Japan
5. Ozawa Obstetrics and Gynecology Clinic; Maebashi Japan
6. Yokota Maternity Hospital; Maebashi Japan
7. Kamioka Obstetrics and Gynecology Clinic; Maebashi Japan