maternal grandmother vs paternal grandmother

maternal grandmother

noun
  • Used other than figuratively or idiomatically: see maternal, grandmother. (This entry is a translation hub.) 

paternal grandmother

noun
  • Used other than figuratively or idiomatically: see paternal, grandmother. (This entry is a translation hub.) 

How often have the words maternal grandmother and paternal grandmother occurred in a corpus of books? (source: Google Ngram Viewer )