How can I conduct meta-regression on prevalence meta-analysis?

After searching,I didn't find any guidelines on conducting meta-regression on prevalence meta-analysis(no treatment group).

Where or how can i make it? here is a data set, after i made an overall estimate and there was heterogeneity(p<.001). How can I use meta-regression to track the source of this heterogeneity. In a priori,I suspected that the prevalence may change with the year,region and maybe high among pregnant women.

set.seed(100)
study<-paste("study",1:70)
events<-sample(1:100,70,replace=T)
studysize<-sample(500:5000,70,replace=T)
studyyear<-sample(1980:2015,70,replace=T)
studyregion<-rep(c("africa","america","asia","europe"),70/4)
studyincludedpregnants<-rep(c("yes","no"),70/2)

#overall estimate library(meta)
m1 <- metaprop(events,studysize)


• I tried this > ess<-escalc(measure="PLO", xi=events,ni=studysize) > meta2<-rma(ess\$yi , ess\$vi , mods=~studyincludedpregnants,method="ML") – Elmahy Feb 3 '16 at 9:47