Answer: Vigorous uterine contractions lead to the delivery of the foetus at the conclusion of an average 9-month pregnancy. Parturition is the term for this process.

The signals from the fully grown foetus and the placenta, which cause the foetal ejection reflex, start parturition, which is a neuroendocrine mechanism. The adrenal glands of a developing foetus release hormones. These chemicals diffuse into the maternal bloodstream and accumulate, causing the posterior pituitary to release oxytocin (the birth hormone).

Oxytocin causes labour pains by causing the smooth muscles of the myometrium to contract violently, pushing the baby out via the dilated cervix (produced by relaxin) and vagina, with the head first. Further oxytocin production is stimulated by uterine contraction. The uterine contraction and oxytocin production stimulate each other, resulting in stronger and stronger contractions. The contraction of abdominal muscles is helped by a reflex and intentional contraction. The foetal membranes burst, releasing amniotic fluid, but the foetal membranes remain.

This stage of ejection can last anywhere from 20 minutes to an hour. The umbilical cord, placenta, and foetal membranes are all evacuated as decidua or after birth during the placental stage, which lasts 10-45 minutes.

The reason for this is that the uterus shrinks after childbirth, forcing the placenta to detach. The umbilical cord is knotted, then cut, resulting in a depression scar known as the umbilicus or navel.