I think you also want to limit the search by "entry type", as it seems the same accession number can be used for datasets, series and samples.

Using the development version of rentrez to demonstrate (though, of course, you can do this with any package). First find what search terms are aviable for GDS:

library(rentrez)
terms <- entrez_db_searchable(db="gds")
as.data.frame(terms)[c("ACCN", "ETYP"),]                                                                 

#ACCN accession for GDS (DataSet), GPL (Platform), GSM (Sample), GSE (Series)
#ETYP                                          Entry type (DataSet or Series)

Then make your search/fetch your summary:

gds_search <- entrez_search(db="gds", term="GSE57214[ACCN] AND gse[ETYP])")
gds_search$ids
# [1] "200057214"

#get the record summary as a list:
entrez_summary(db="gds", id=gds_search$ids)