Parturition

Parturition is the process, collectively called labour, that completes pregnancy by expelling the baby from the uterus. The uterus is not entirely quiet before this: throughout pregnancy it already undergoes periodic weak-to-moderate contractions known as Braxton-Hicks contractions, sometimes felt as 'false labour.' As pregnancy nears full term, rising oestrogen concentration (relative to progesterone) makes the uterus increasingly prone to contract, and genuine contractions begin, gradually moulding the foetus and moving it downward. This descent stretches and dilates the cervix and vaginal canal, and that stretching sets off a neurohumoral reflex known as the foetal ejection reflex or Ferguson reflex, which causes the posterior pituitary (neurohypophysis) to release oxytocin. Oxytocin, in turn, drives the powerful, coordinated contractions of the uterine muscle that finally expel the baby through the birth canal — this whole hormone-driven sequence is what is meant by parturition or childbirth. Relaxin, secreted both by the placenta and by the corpus luteum, works alongside this process by relaxing the pelvic joints and assisting further dilation of the cervix under the ongoing contractions. After delivery of the baby, the placenta and the remaining portion of the umbilical cord are also expelled, together referred to as the …