Funding for this research was provided by:
the Science and Technology Project of Health and Family Planning Commission of Sichuan Province (17PJ506)
Luzhou Medical College Science Foundation (2014QN-048)
Received: 14 March 2019
Accepted: 22 October 2019
First Online: 7 November 2019
Ethics approval and consent to participate
: The study protocol was approved by the Ethics Committee of the Affiliated Hospital of Southwest Medical University (project no. K2016004). This is a retrospective study. The need for informed consent was waived by the Clinical Research Ethics Committee.
: Not applicable.
: The authors declare that they have no competing interests.