1. Department of Obstetrics and Gynecology, Sakakibara Heart Institute, Tokyo, Japan;
2. Department of Obstetrics and Gynecology, Mie University School of Medicine, Mie, Japan;
3. Department of Obstetrics and Gynecology, St Marianna University School of Medicine, Kanagawa, Japan;
4. Department of Obstetrics and Gynecology, Showa University School of Medicine, Tokyo, Japan;
5. Department of Obstetrics and Gynecology, Hamamatsu University School of Medicine, Hamamatsu, Japan;
6. Department of Obstetrics and Gynecology, Toho University, Tokyo, Japan;
7. Division of Perinatology, Maternal and Perinatal Care Center, Seirei Hamamatsu General Hospital, Hamamatsu, Japan;
8. Department of Perinatology and Gynecology, National Cerebral Cardiovascular Center, Osaka, Japan;
9. Ishiwata Obstetrics and Gynecology Hospital, Ibaraki, Japan