afterbirth vs placenta

afterbirth

noun
  • The placenta and other material expelled via the birth canal following childbirth or parturition in mammals. 

placenta

noun
  • An organ in most mammals during gestation that supplies food and oxygen to the foetus and passes back waste. It is on wall of the uterus and links to the foetus through the umbilical cord. It is expelled after birth. 

  • In flowering plants, the part of the ovary where ovules develop; in non-flowering plants where the spores develop. 

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