The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex.

This triggers the release of of oxytcin from the maternal pituitary..which acts on the uterine muscle and causes stronger uterine contractions.The stimulatory reflex btw the uterine contraction and oxytocin secretion continues resulting in stronger contractions.This leads to expulsion of the baby through the birth canal,i.e parturition.