Funding for this research was provided by:
National Natural Science Foundation of China (81773489)
Social Science and Technology Innovation Subject in Chongqing (cstc2015shmszx120070)
Technology Basic and Advanced Research Projects in Chongqing (cstc2014jcyjA10069)
Project from Health and Family Planning Commission of Guizhou Province (gzwjkj2015-1-079)
Received: 28 January 2019
Accepted: 28 May 2019
First Online: 2 July 2019
Ethics approval and consent to participate
: The project proposal was approved by the Institutional Review Board of Army Medical University, Chongqing, China. Written informed consent was obtained from all participants once they agreed to take part in the study.
: Not applicable.
: The authors declare that they have no competing interests.