If you have been following us closely, chances are we have mentioned cervix once too many.
But, exactly, what does the cervix do and where is it?
Where is it?
You probably have a vague idea where the cervix is – it is ‘down there but up a bit’, right? In fact, it is the lower part of your uterus that extends in your vagina, which is why it is often called the ‘neck of the womb’. Think of it as the connection between your uterus and vagina.
What does it do?
The cervix is actually a very busy part of your body, even before its very important job during labour. After your period ends, your cervix is blocked by a thick acidic mucous that prevents infection.
During most of your menstrual cycle your cervix remains firm, like the tip of the nose, and is positioned low and closed. As you approach ovulation, your cervix becomes soft, then rises and opens due to higher levels of oestrogen. During this stage the mucous thins to allow semen to pass through your cervix to the Fallopian tubes, where they wait for an egg to be released. The cervical mucous reverts to a thicker form shortly after ovulation occurs.
This change in mucous texture is important in natural family planning methods, which requires careful observation of vaginal discharge to determine the fertile and infertile times of your cycle.
When you are pregnant, your cervix is blocked by a special mucous plug that prevents infection, similar to what occurs during the infertile part of your menstrual cycle. The mucous plug comes out as the cervix dilates in labour, or shortly before.
As a pregnant woman, it is the cervix’s ability to dilate that probably interests you most. How does it know what to do? The cervix normally receives specially coordinated hormonal messages in the middle of the third trimester of a normal pregnancy. These hormonal messages lead to a softening of the cervical tissue that is accompanied by an increased elasticity and ability to gradually distend, due to a change in the elastic tissue within the cervix.
Before you go into labour your cervix is about 3cm long and closed. When your contractions begin, your cervix will start becoming shorter (this is ‘effacement’) and will dilate. The cervix is fully dilated when it has opened to 10cm. Once it has reached this point the first stage of labour is over, and you are now ready to push.
What can go wrong?
Most women will go through their pregnancies without having to think about their cervix. Some, however, will have what is known as an incompetent cervix. This is a relatively uncommon problem in pregnancy where the cervix begins to dilate very prematurely, often as early as 18 to 20 weeks gestation.
This is a serious condition, often with fatal consequences, due to the fact the mother will go into premature labour well before 24 weeks. This generally results in a miscarriage, though there have been cases of premature babies surviving this young.
Unfortunately, most women would not know they have an incompetent cervix until they are pregnant and experience the trauma.
So what causes it?
There are a number of recognised issues, but there are also cases where there is no recognisable predisposing problem. Occasionally, the problem can be congenital – this is often associated with a double uterus, or some other congenital abnormality of the upper part of the uterus. It may also follow treatment for pre-cancerous cells (usually following a procedure called a cone biopsy). It can also occasionally follow other operations that result in the stretching of the cervix for a medical procedure, although this is very unusual.
Some women may also suffer from a short cervix. This may be a different problem but it can sometimes result in ‘incompetence’ with premature dilation of the cervix mid-pregnancy.
What can you do?
If you had an incompetent cervix in the past, some doctors like to perform a ‘cerclage’ for subsequent pregnancies. This is a surgical stitch that helps support the cervix during pregnancy.
It is generally put in place towards the end of the first trimester then removed a couple of weeks before the baby is due. It may sound scary but it is usually a fairly straightforward procedure.
Generally, your doctor would also prescribe bed rest to minimise any further risk before the baby is born, and would probably recommend that you and your spouse avoid having sex until your baby arrives.