Funding for this research was provided by:
National Natural Science Foundation of China (81870595)
Major special projects of hunan provincial health and family planning commission (A2017011)
Received: 6 February 2018
Accepted: 9 January 2019
First Online: 22 January 2019
Ethics approval and consent to participate
: The study protocol was approved by the Ethics Committee of the First Affiliated Hospital of University of South China, and written informed consent was obtained from all participants before their inclusion in the study.
: Not applicable.
: The authors declare that they have no competing interests.
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