1. Department of Obstetrics and Gynecology; Niigata University Graduate School of Medical and Dental Sciences; Niigata Japan
2. Department of Obstetrics and Gynecology; Joetsu General Hospital; Joetsu Japan
3. Department of Obstetrics and Gynecology; Tachikawa Hospital; Nagaoka Japan
4. St Mother Hospital; Kitakyushu Japan
5. Niigata Medical Center Hospital; Niigata Japan