Received: 12 January 2021
Accepted: 10 September 2021
First Online: 18 September 2021
: This study was performed as an investigation of JAOG and approved by the ethics board of JAOG (No. 80, 1 July 12 2020). This investigation was conducted in accordance with the principles of the Declaration of Helsinki. Because this was a retrospective analysis based on a questionnaire survey, all patient records and data were anonymised by the institutions prior to submission for analyses and the need of informed consent was waived by the ethics board of Japan Association of Obstetricians and Gynecologists (JAOG).
: Not applicable.
: None to report.