lying-in vs vaginal birth

lying-in

noun
  • The final stages of pregnancy; accouchement. 

  • A period of postpartum confinement, typically a month or longer, formerly common in Europe and still practiced in some parts of the world. 

adj
  • of, or relating to childbirth or postpartum confinement 

vaginal birth

noun
  • Birth via the vagina (as opposed to caesarean section). 

How often have the words lying-in and vaginal birth occurred in a corpus of books? (source: Google Ngram Viewer )