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Although the process is not entirely understood, scientists believe the hormone CRH and CRH binding proteins are responsible for regulating labour, as they induce placental release of estrogen and localised release of prostaglandins. Levels increase exponentially throughout pregnancy, and tend to be higher in mothers who give birth preterm.
Although the process is not entirely understood, scientists believe the hormone CRH and CRH binding proteins are responsible for regulating labour, as they induce placental release of estrogen and localised release of prostaglandins. Levels increase exponentially throughout pregnancy, and tend to be higher in mothers who give birth preterm.
===Stages===
'''Stage One''' is associated with the start of painful contractions and the dilating of the cervix. Contractions are initially slow until the cervix reaches a diametre of 3cm, then the increase in speed until the end of stage one, at which point the cervix is at a diametre of approximately 10cm. Each muscle cell does not completely relax, and therefore shortens with each contraction. The retraction ring gradually moves upwards.
'''Stage Two''' is associated with the delivery of the foetus. As the foetus moves down it is rotated due to the dimensions of the pelvis (ellipsoid laterally at the pelvic inlet, circular in the middle and ellipsoid medially at the pelvic outlet). This generally results in the baby's head facing the mother's rectum. Abdominal contractions assist with the expulsion of the child.
'''Stage Three''' is associated with the delivery of the placenta. Because of the importance of completely removing the entire placenta (abandoned villi can result in maternal haemorrhage) this stage is usually assisted with steady traction on the umbilical cord and doses of oxytocin.