Received: 20 February 2021
Accepted: 30 March 2021
First Online: 8 April 2021
: This study was approved by the institutional review board of the National Defense Medical College, Tokorozawa, Japan (approval no.3084). Records/information of all women in the study were completely anonymized and de-identified prior to analysis. The present study was exempt from collecting informed consent from all participants.
: Not applicable.
: All authors declare that they have no conflicts of interest.