one’s level best vs travail

one’s level best

travail

verb
  • To toil. 

  • To go through the labor of childbirth. 

noun
  • Arduous or painful exertion; excessive labor, suffering, hardship. 

  • Specifically, the labor of childbirth. 

How often have the words one’s level best and travail occurred in a corpus of books? (source: Google Ngram Viewer )