A normal pregnancy is anywhere from 37 – 42 weeks. It is not completely understood how labour starts, but the baby does initiate labour by sending endocrine signals to the placenta to produce enzymes that stimulate production of oestrogen. Labour is exciting, challenging and can be stressful for both the woman and her baby. As a result hormones pour into her bloodstream and gives the labouring woman a ‘high’ or a ‘buzz’. Exercisers and athletes often talk about these ‘highs’, which enable them to climb the highest mountain, complete the marathon, swim the 1500 metres. There is a striving and longing to give your utmost, and the thrill of the
unknown. It is like that when labour begins. These hormones are produced by both the woman and the baby. In fact, the baby produces them in vast quantities.
The hormonal changes that the baby has started now stimulate the beginning of an amazing process. The uterus produces prostaglandins and as a result contractions/surges begin to feel much stronger than the Braxton-Hicks ones. These more efficient surges/contractions press the baby’s head down on to the base of the lower segment of the uterus and against the cervix. This then becomes progressively more stretched and thinned out as the muscle fibres are pulled up into the upper segment. The effacement and stretching of the cervix trigger the production of oxytocin from the posterior pituitary gland, and this stimulates the uterus into a steady rhythm of waves, often referred to by midwives as ‘established labour’
Before labour starts, the baby is lying with his head resting in the pelvic brim, ready for birth. The cervix of the uterus is closed and sealed by a mucous plug. In the last couple of weeks of pregnancy the cervix becomes soft and ripe and ready for opening up.