1 Department of Obstetrics and Gynecology, Jichi Medical University, Tochigi, Japan. Electronic address: ytakahashi@jichi.ac.jp.
2 Department of Obstetrics and Gynecology, Jichi Medical University, Tochigi, Japan; Department of Obstetrics and Gynecology, Koga Red Cross Hospital, Ibaraki, Japan.
3 Department of Obstetrics and Gynecology, Jichi Medical University, Tochigi, Japan.