1 Department of Obstetrics, Hokkaido University Graduate School of Medicine, N15W7, Kita-ku, Sapporo 060-8638, Japan. Electronic address: taka0197@med.hokudai.ac.jp.
2 Department of Maternal-Fetal and Neonatal Medicine, National Center for Child Health, Japan.
3 Department of Obstetric and Gynecology, School of Medicine, Kitasato University, Japan.
4 Department of Obstetric and Gynecology, Nippon Medical School, Japan.
5 Department of Obstetric and Gynecology, Jichi Medical University School of Medicine, Japan.
6 Graduate School of Medicine and Pharmaceutical Science, University of Toyama, Japan.
7 Department of Obstetrics, Hokkaido University Graduate School of Medicine, N15W7, Kita-ku, Sapporo 060-8638, Japan.