The process of childbirth, known as labour, begins at about the 40th week of pregnancy. There are three distinct stages of labour: first, the contractions in the uterus and the widening of the cervix; second, the birth of the baby; and finally, the delivery of the placenta. The length of each stage varies between women and may depend on the number of previous pregnancies.
Labour begins when regular contractions start. The passing of the mucus plug from the cervix occurs up to 10 days before the start of contractions. The amniotic sac that surrounds the baby ruptures either shortly before or at any time during the first stage of labour. The first stage of labour lasts on average 6–12 hours.
The passing of the mucus plug from the cervix is known as the show. It is a signthat labour is soon to start, but it goes unnoticed by many women.
Contractions begin at any time in the few days following the show. With each contraction, the uterine muscles shorten and thicken.
The contractions gradually become stronger and more regular. By this stage, the amniotic sac has usually burst.
During the second stage of labour, the baby travels from the uterus down the vagina and is born. This stage is much quicker than the first stage and usually lasts 1–2 hours. The cervix is fully dilated, and the uterine contractions are very strong and usually painful. The baby’s head presses down on the pelvic floor, which causes the mother to have an overwhelming urge to push down. Once the baby’s head is visible at the vaginal opening, the birth is imminent.
As the mother starts to push, the baby turns towards the mother’s back and begins to move out of the uterus, with its head bent on to its chest. The vagina, or birth canal, stretches as the baby descends.
Just before the baby is born, it turns again. The head rotates so that it can negotiate the bend in the vagina. The baby is usually facing the mother’s anus as it leaves the vagina.
As the baby’s head emerges, the midwife or doctor checks that the umbilical cord is not wrapped around the neck and clears any mucus from the baby’s nose and mouth. The rest of the body slides out easily. The umbilical cord is then clamped and cut.
During the third stage of labour, the placenta is expelled from the uterus. The placenta peels away from the lining of the uterus and is gently pushed through the vagina and out of the body. Often, the mother is injected with a drug that helps the muscles of the uterus to contract and so stop any bleeding from the site where the placenta was attached.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.