Funding for this research was provided by:
Japan Society for the Promotion of Science (16H05225)
Received: 14 September 2019
Accepted: 8 January 2020
First Online: 16 January 2020
Ethics approval and consent to participate
: All of the women provided written informed consent for this study. The study was approved by both the ethics committees of the Toho Obstetrics and Gynecology Hospital and the Faculty of Health Sciences, Hokkaido University (15–99-5).
: Not applicable.
: The authors declare that they have no competing interests.