Funding for this research was provided by:
National Natural Science Foundation of China (81202220)
Natural Science Foundation of Jiangsu Province (BK20150094)
Chongqing Health and Family Planning Commission (20141027)
Received: 28 January 2019
Accepted: 7 May 2019
First Online: 3 June 2019
Ethics approval and consent to participate
: Ethical approval was not applicable for this systematic review and meta-analysis.
: Not applicable.
: The authors declare that they have no competing interests.
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