The cervix is the neck or opening to the uterus. It is approximately 2.5cm long and extends down into the vagina at a slight angle, pointing towards the back of the vagina (posteriorly behind the baby's head) until labour or prelabour starts. With contractions the cervix starts to move towards the centre or front of the woman's vagina as it thins and dilates or opens.
How the cervix changes
A woman's cervix changes in subtle ways during her menstrual cycle as well as during pregnancy. As the pregnancy progresses, the cervical tissue becomes very glandular, producing a mass of thick mucus that plugs the cervical canal called a mucus plug or 'show'. This seals the uterus from outside infection. The show often comes away, mixed with a little blood during late pregnancy or during labour.
Each individual woman's cervix can have small noticeable changes during pregnancy. For some women their cervix remains very closed, for others it can be slightly dilated (admitting a finger) but still remain quite thick. These changes are normal as it is only when the cervix thins out before dilating significantly that it indicates labour is starting.
During the last few weeks of pregnancy it is not unusual for a woman's cervix to be thick but slightly dilated from 1 to 3 centimetres, due to heavy pressure from the growing baby. The cervix can also soften (from being firm) as it prepares for labour. A slightly dilated, soft cervix during late pregnancy does not necessarily mean the labour will start early (or be shorter). The cervix can be like this for several weeks before the birth. For other women their cervix can remain very firm and closed until prelabour or labour starts and then change rapidly within hours of having mild or moderate contractions. Having a closed, firm cervix during late pregnancy (especially if this is your first baby) is very normal and does not necessarily mean that your baby will be overdue or that your labour will be longer.
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