Funding for this research was provided by:
Scientific Research Fund of Health and Family Planning Commission of Shanxi Province (2016C005)
Received: 22 March 2019
Accepted: 20 May 2019
First Online: 13 June 2019
Ethics approval and consent to participate
: The study was approved by the ethics committee of the Hanzhong Central Hospital (#IRB2018-S; April 12th, 2018). The need for individual consent was waived by the committee because of the retrospective nature of the study.
: Not applicable.
: The authors declare that they have no competing interests.
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