The process of delivery of the foetus is called parturition. It is induced by a complex neuroendocrine mechanism. The signals of parturition originate from the fully developed foetus and the placenta. These signals induce mild uterine contractions; called foetal ejection reflex. This triggers the release of oxytocin. Oxytocin acts on the uterine muscle and causes stronger uterine contractions. The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contractions. This leads to expulsion of the baby out of the uterus through the birth canal. After the infant is delivered, the placenta is also expelled out of the uterus. Before pregnancy, a woman’s uterus is typically the size of an orange. By the time of parturition, it becomes about the size of a watermelon. In fact, it can expand up to 500 times the size during pregnancy. Watch this video to learn more about parturition.
Human Physiology – Parturition