You’ve probably heard talk of “10cm dilated”, but what exactly is dilating, and what does it mean when care providers talk about cervical dilation during labour?
The basics of cervical dilation
Dilation (noun): the act or action of enlarging, expanding, or widening
During your pregnancy, your cervix, which is simply the entrance to the uterus, is tipped towards the back of your body, hard to the touch, thick, and closed. It is also covered up by a plug of thick mucous which is designed to stop any infection entering your uterus.
In order for your baby to be born, the plug of mucous needs to move out of the way and the cervix must tip towards the front of your body, think and open wide enough for your baby to pass through and down the birth canal. The part of the process during which the cervix opens is called dilation.
The process of cervical dilation
As your body begins to get ready for labour, the mucous plug may fall away and you may see evidence of this in your knickers. The plug may come away all at once, in parts or not at all. The mucous is usually thick and jelly-like, and may not be completely clear. It may also be streaked with small amounts blood. This is normal and is known as a bloody show. Some women do not notice the loss of their mucous plug at all.
The cervix and uterus, meanwhile, start to gear themselves up for labour. The cervix thins and dilates as contractions begin in the uterus. There are three layers of muscles in the uterus. The most important for labour are the layer of vertical muscles and the layer of horizontal muscles that are stacked in a ring-like formation in the uterus. As labour begins, the vertical muscles in the uterus begin to pull up the horizontal muscles, which causes the cervix to thin and begin to open (dilate).
As labour advances, more muscle mass is concentrated at the top of the uterus and the cervix opens more and more until the presenting part of your baby (usually the head) is able to pass through the space.
So what does it mean when someone talks about being “5cm dilated”?
If you are planning on giving birth in hospital, you will be offered regular vaginal examinations. This is where the midwife puts their fingers inside your vagina to feel the cervix and to estimate how much it has opened up. As the cervix is simply a ring of muscle, the number of centimetres that your midwife tells you refers to the estimated radius (the width of the opening at its widest point).
So when you are told that you are 4, 5, 6, etc. centimetres dilated, this refers to how open your cervix is.
The usual figure given for when a woman is fully dilated is 10cm. This can feel a bit alarming when you are sat at home looking at a ruler. What’s most important to remember is that your cervix is going to open just as much as it needs to to let the widest part of your baby’s head pass through, and no more than that. For some women this may well be 10cm, for others it will be less.
Will my cervix dilate at a steady rate?
In short, no. Birth is a physiological process. I like to compare it to puberty – everyone hits puberty at a different age and puberty changes everyone’s bodies at a different rate. For some people it starts early and is slow and drawn out, others are late bloomers and experience a fast and furious array of changes to their bodies.
The birthing body is as unpredictable as the body going through puberty.
The cervix may open at a slow and steady pace, it may open very quickly, it may start off opening very slowly and then suddenly go from half open to fully open in the space of an hour, or vice versa. There’s no predicting how your cervix will open.
Why do midwives want to check my cervix then?
To understand why vaginal examinations have become part of routine antenatal care, it’s necessary to go back in time to the middle of the last century.
In 1955, an American obstetrician called Emmanuel Friedman published a study investigating the association between labour duration and cervical dilation. He plotted the labours of 500 mothers who gave birth at full term on a graph and calculated the average time it took a woman’s cervix to dilate each centimetre. The graph became known as the Friedmans curve and has been used as the ‘gold standard’ for cervical dilation ever since.
It is essential to note that the sample that Friedman studied was made up of 100% first-time white mothers. a large proportion of the women were sedated and the sample included breech births, twin births, still births and assisted births. It is important to remember, too, that the curve shows the average rate of dilation of the women. Some women dilated more quickly to begin with and then slowed down or vice versa.
Despite the sample used, which falls well below today’s scientific standards, the Friedmans curve is still applied to labour as a way of measuring progress. There is an expectation in mainstream settings such as hospitals, that, once you are in active labour (over 4cm dilated), your cervix should dilate at a rate of approximately 1-2cm every 2 hours. If it does not, you labour may be labelled with “failure to progress” and artificial augmentation (speeding up) of labour may be suggested.
So, to return to the original question, midwives want to check your cervix at regular intervals to find out whether your labour is progressing “as it should”. However, as I discussed earlier, labour is a physiological process, and many women will not dilate at a steady rate of 1cm per hour in active labour. There is even anecdotal evidence of women whose cervixes, which were opening nicely, closed up during labour because of the presence of someone unwanted in their birthing room.
What can I do to make sure that my cervix dilates well?
Ultimately, you cannot actively control the rate at which your cervix will dilate. However, there is plenty you can do to encourage your body to labour well and your cervix to dilate. For example:
- Relax your jaw – tension in the jaw is linked to tension in the cervix so relaxing it will help your cervix to dilate more easily.
- Make your nest – whether you are labouring at home or in hospital, create your nest. Your body will labour better when it is calm and relaxed, so surround yourself with things that make you feel good: photos of your loved ones, scents you like, music that makes you vibe etc.
- Stay upright and move* – gravity is your friend during labour, and you may find yourself naturally moving through the contractions as your body looks to make more space in your pelvis for your baby to descend.
*unless you are tired, in which case listen to your body and have a rest!
Want to know more?
Found this fascinating? Learn even more about cervical dilation, vaginal examinations and labour, as well as how you can support your mindset by joining a hypnobirthing course. Group and private courses are available virtually and in person around Otley, West Yorkshire.
Other resources
Vaginal Examinations: Stuck in the Cervix – blogpost by Dr Rachel Reed which examines the origins of cervical examinations and the evidence behind their routine use in obstetric settings.