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Know how: what is dilation?

You might have heard about women being 'three centimetres dilated' and so on, but what exactly does it all mean?


Posted: 11 September 2009
by Laura Lee Davies


By the time you are due to have your baby, you are usually familiar with the jargon of labour and birth, but sometimes it's easy to use the language without fully understanding it.
Midwives and doctors will probably seem obsessed with two factors - how often and intense your contractions are, and then how far you have 'dilated'. So what does 'dilation' mean?

What is dilation?
During your pregnancy, unless you have experienced problems with what is classed an 'incompetent cervix', your cervix will have acted as the 'cork' to your uterus. It keeps the fetus and amniotic fluid in place in the womb.
As the birth approaches, the cervix will gradually 'ripen' and this thick neck of the uterus begins to thin out (this is called effacement) to allow the cervix to open up so that the baby can pass through it during the birth.
Dilation is the process of the cervix opening up. By the time you are 'ten centimetres dilated', you are ready for the birth. (For the various stages of labour, click here.)

When and how does dilation occur?
For many women, the earliest stages of dilation – up to three centimetres – can happen over a period of days or even weeks, and may well not be noticeably painful.
If this has not happened, this first stage of dilation may occur with noticeable brief contractions (of about half a minute each time, and spread out with quite a gap between them) at the very start of your labour. If so, it might take about two to five or six hours for the first three centimetres' dilation.
Despite this opening up, your waters may not neccessarily break until later.
If you have not noticed the early dilation, you will be more aware of the next phase, as the contractions become longer, more frequent (though possibly still not regular) and more intense. This period tends to last about two or three hours and during this time, the cervix may dilate to about seven centimetres.
Depending on the midwife team involved, you will have been advised to go to hospital sometime between the first and second more intense stage.
After gauging how frequent your contractions are, a midwife or doctor may perform an internal examination to see how 'dilated' you are. If your waters have not broken yet and you are at least five centimetres dilated, your waters may be broken to bring things along if it is felt that your labour is slowing. However, sometimes your midwife may not need to do this if the medical team are happy with your progress.
As your contractions get more painful and last longer, you will dilate the last three centimetres. Happily, this end process usually lasts for less than an hour!
When you are fully dilated a 10cm, your midwife or doctor will soon tell you that it is time to 'push'.


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