The pooled risk difference (RD) as well as their 95% confidence interval (CI) were calculated by RevMan 5.3 software.



RevMan
A literature search was conducted in Google scholar, PubMed, Embase, and Web of Science databases up to February 2019. 
Google scholar
A literature search was conducted in Google scholar, PubMed, Embase, and Web of Science databases up to February 2019. 
PubMed
A literature search was conducted in Google scholar, PubMed, Embase, and Web of Science databases up to February 2019. 
Embase
A literature search was conducted in Google scholar, PubMed, Embase, and Web of Science databases up to February 2019. 
Web of Science