In humans, oxytocin

Parturition is a process of delivering the baby and placenta to outside of the body.

The signals for parturition originate from the fully developed foetus and the placenta that induce mild uterine contraction are called foetal ejection reflex. This reflex triggers release of oxytocin from the maternal pituitary.

Oxytocin stimulate strong uterine contraction in labor and childbirth and also stimulate contraction of breast tissue to aid in lactation after childbirth.