Funding for this research was provided by:
the Japan Society for the Promotion of Science (JSPS) KAKENHI (18K09006)
Received: 7 July 2019
Revised: 5 September 2019
Accepted: 24 September 2019
First Online: 8 November 2019
Compliance with ethical standards
: Ethical approval was obtained from the ethics committee at Tokyo Women’s Medical University (No. 3540).
: Given the retrospective design, the institutional review board waived the requirement for informed consent. We took the opt-out method. To protect patient privacy, we removed all identifiers from our records upon completion of our analyses.
: The authors declare that they have no conflict of interest.