Cervical Dilation: 12 Fun Facts

Almost everyone knows that one important aspect of labour is that the cervix has to dilate from zero to ten centimetres. But what does this actually mean? What is the cervix, how does it dilate, and how does that relate to your birth? And more importantly, does it hurt? Here are twelve things you might not know about the cervix and dilation.

  1. The Cervix Is The “Neck” Of The Uterus

    The word “cervix” means “neck” in latin, and indeed the cervix is like the neck of the uterus. It is not a free-standing organ, but rather the passageway to the lower part of the womb; the gate where the baby comes out.

  2. Cervical Dilation Doesn’t Hurt

    I frequently see people cringe when they hear that their cervix has to dilate from 0 to 10 cm. Picturing that size of change in a body part can seem intimidating, especially if you’re imagining that something otherwise small will be STRETCHED beyond its normal capacity. But cervical dilation is more like slowly opening a closed mouth. The cervix doesn’t really stretch so much as rearrange itself. Most people don’t feel it at all. There are many aspects of labour that you feel intensely, but cervical dilation isn’t usually one of them.

  3. It’s Not Really 10 Cm

    The cervix doesn’t need to open to any particular magical number, and no one will get a ruler anywhere near your cervix during labour. The cervix just needs to clear your baby’s head–to open around your emerging baby–to allow your newborn to pass through. Ten centimetres simply represents the ‘average’ baby. Your baby’s head could be smaller or larger than that. However, just to be confusing, the term “10 cm dilated” is used as a metonym, a substitute way of saying “fully dilated”, even though it doesn’t necessarily mean a literal measurement of ten centimetres.

  4. The Cervix Also Changes Position

    The cervix doesn’t only dilate during labour. It also moves forward to line up with the birth canal. Prior to labour, the cervix angles slightly back, pointing towards your tailbone, but for labour it shifts forward to line up with the vagina. You can’t feel this at all either. And your cervix does this same little journey as part of your monthly fertility cycles, so you’re already a pro.

  5. The Cervix Also Changes Texture

    Another change your cervix experiences during labour is that it softens. Softening (also called ripening) is quite dramatic. The cervix gradually shifts from a rigid, cartilage-like texture to a soft, flexible texture throughout labour. It’s like the difference between your nose (firm) and your lips (flexible). Or like toffee at fridge temperature versus when it has been warmed on a stove. Or like how stiff, brittle clay gets softer and more malleable the more you knead it. The normally solid, rigid cervix becomes increasingly ripe and flexible until it is loosy-goosy and supple. By the end of labour, the cervix is ‘butter soft’--extremely yielding and pliable.

  6. The Cervix Also Changes Length

    Yet another thing your cervix does during labour is shorten (also called effacing or thinning). It begins long, and gradually gets shorter and shorter below the baby’s head. This happens concurrently to softening, and each of these changes helps the other. The softer the cervix, the more easily it shortens, and the shorter the cervix, the more easily it softens. 

  7. Dilation Tends To Speed Up 

    These two shifts also happen in tandem with dilation, each aspect of cervical change contributing to the efficiency of the others. Dilation is propelled by the cervix softening and thinning. In early labour, dilation is extremely slow. You may have heard that early labour is usually much longer than active labour? This is true. It is not uncommon to labour for many hours at the beginning with minimal cervical dilation. This is because the cervix has so many jobs to do at once, and may pause on one (such as dilation) while it prioritizes another (such as thinning). But a bigger reason is that the previous cervical changes all contribute to an increasing rate of dilation. When the cervix is still rigid and firm, it takes much time and more effort for your contractions to budge its diameter. Picture how much more time it takes to alter the shape of hard clay (or butter, or dough, or toffee), compared to when it’s softened. 

    Similarly, a long, cylindrical cervix is harder to open. Picture a 5 cm tube-shaped rubber band, and how much strength it would take to open it with your hands. Now picture a paper-thin, skinny elastic band, and how easy it is to stretch it wide. A shorter cervix, likewise, is much more prone to opening with less effort. This helps illustrate why it might take 50 contractions in early labour to effect the same amount of cervical change as a single contraction near the end of labour: this contributes to why dilation typically happens faster when you’re further along. 

    The important point here is to try not to be discouraged by low numbers. Most cervical exams yield low numbers, because once labour really kicks in and speeds up, fewer are done. It is common to dilate very, very slowly at first. This has no bearing on how quickly you will dilate once the pace picks up. Remember, each phase of first stage labour (early, active, and transition) represents an equal third of the total 10cm dilation, but not an equal third of time. Early labour (the first 3 - 4 cm) usually takes longer than the other two phases put together, whereas transition (the final 3 - 4 cm) usually happens very quickly. Most people have hundreds of early labour contractions, compared to only a handful in transition. The pace of dilation does not at all track with the pace of time.

  8. Dilation Can Also Pause

    As mentioned above, it is common and normal for there to be no dilation over irregular periods of time. This does not necessarily mean labour has stalled, but simply that other forms of progress are happening that might be less measurable. Your labour could be working on thinning or softening the cervix, or repositioning the baby, or stockpiling more labour hormones, or doing something we’ll never know about, or sometimes just taking a rest before summoning more energy. Any of these efforts might result in a big jump in cervical dilation afterwards. Given that cervical dilation is one of the only measurements that gets tracked and recorded, it limits our viewpoint of the broad scope of changes that labour encompasses, including the intricate and complex structures of hormonal scaffolding. This can lead to concerns around labour ‘stalling’ during natural rest periods in dilation, simply because we can’t see all the other things that might be going on.

  9. Cervical Changes May Begin Before – or After – the Onset of Labour

    Another interesting aspect of cervical dilation is that it can begin before you start feeling contractions, sometimes even days – or weeks – before. The elaborate structure of hormones that begins to build in the final phase of pregnancy starts softening, thinning, and even dilating the cervix in preparation for labour, so that some people can be walking around at 2 or even 3 cm dilated for days, and occasionally even a week or two, before experiencing any palpable signs of labour. This is normal and fine, and if you discover that you are already a little bit dilated (like at a routine midwife or doctor appointment), no action is required. Unless advised otherwise, most people can keep on with normal life until you start feeling contractions. The opposite can also happen, of course, where contractions can precede cervical dilation. Some people have contractions for many hours, or even a full day or more, prior to any dilation. In this case, the cervix would usually be working on thinning and softening before doing any opening. But these are all normal variations. All the cervical and hormonal changes of labour work in nuanced tandem, and anything we observe or measure is just a snapshot of a highly complex choreography.

  10. What Is Being Measured Changes

    Another interesting note about understanding cervical dilation is that the actual unit of measurement changes at some point, which can sometimes affect the results. In early labour, cervical dilation is assessed by a care provider (doctor, midwife, or nurse) feeling the size of the cervical opening with their fingers. This is a manual internal exam, and like any vaginal exam, it can feel uncomfortable, invasive, and disruptive. At this stage, because the cervix is still long and rigid, they can only assess the opening, and they can blindly ballpark its size in centimetres based on the gap they feel with their fingers. But as the cervix opens, it is also thinning. Eventually, usually somewhere around the 5 cm range, the cervix is effaced enough that the care provider can now feel how much cervix remains to dilate more easily than they can feel the gap that’s already dilated. The gap is now too wide to easily feel the edges at the same time, but the amount of cervix still on the baby’s head is now more accessible to reach. So the unit of measurement usually switches. And this can sometimes change the interpretation of how advanced your dilation is. For example, someone who was measuring 5 cm based only on the gap, might suddenly measure 7 cm based on how much cervix is left to go. This does not necessarily represent a big jump in dilation so much as a new understanding of how much cervix remains that has yet to yield around the baby’s head. Maybe the baby has a very thin head. Or, conversely, the assessment could switch from 5 cm to 4 cm if there is a lot of baby head still covered, because as we established above in point 3, the cervix doesn’t really have to reach 10 cm, it just has to clear your particular baby’s head. So the initial measurement of the gap is an addition towards an assumed goal of 10 cm, whereas the later measurement of the remaining cervix is a subtraction from an assumption of 10 cm, but the two measurements don’t always meet in the middle. In a sense, the later measurements are more accurate because they start from your own baby’s head, rather than some arbitrary average number. 

  11. The Uterus Rearranges Its Shape

    As the cervix softens, thins, and dilates, it clears from around your baby’s head. It retracts completely, so that when you’re fully dilated, your care provider can’t feel any cervix around the baby’s head at all. The cervix disappears. But where does it go? As it inches outward, the entire uterine muscle is inching upward, moving away from below the baby’s head to above the baby’s bottom, gathering muscle mass at the top of the uterus. Throughout pregnancy, the uterine muscle is mostly congregated at the cervical end, below the baby’s head, putting all its muscle effort into keeping the baby in. But over the course of labour, the uterine muscle retracts from around the baby’s head, regrouping its fibers to the top of the womb, thickening the upper part of the uterus exactly as it thins the lower part. This makes the contractions stronger, with more downward force as labour progresses. Remember point 7 above? Another factor causing dilation to speed up is that the contractions get increasingly powerful and effective – strong and efficient – as the upper part of the uterus thickens with more and more muscle mass. Throughout labour, the uterus rearranges its shape, altering its very function from embracing the baby to evicting the baby. The fact that the cervix dilates is a by-product of this uterine metamorphosis. One might picture dilation as a gate opening, or doors sliding apart, but dilation is more like a secondary effect of this overall restructuring of the womb, as it pulls itself away from the baby’s head to regather above the baby’s feet. Its job now is to push the baby out.

  12. Dilation Can’t Predict The Future

    It is now hopefully clear that how dilated you are can’t predict the future. How dilated you are does not tell anyone when your baby is going to be born. Your cervical dilation represents one limited snapshot of how retracted the cervix is at that moment, but doesn’t tell us what will happen next, or when. Sometimes vaginal checks are truly necessary to assess if something is wrong, for triage reasons, to determine the baby’s position, to see if you meet a hospital’s admission standards, or for many other possible reasons. And sometimes cervical checks are just offered pro forma, or in case you’re curious. You can always ask your doctor or midwife if it’s necessary or if you can skip this one, and they will let you know. There are many important reasons why your team might want to check how dilated you are, and they can explain that when you ask. But if you want to keep the cervical exams to a minimum, that’s usually fine too. Sometimes people ask their care provider to avoid saying the number because it can lead to unnecessary disappointment, given that low numbers are so normal and don’t actually mean labour will continue to advance at such a slow pace. If you ask, some care providers are happy to provide a vague description of your cervical assessment without revealing a number, such as “there’s good cervical change happening, you’re making progress, you’re doing great, just carry on and I’ll come back in a while”, rather than saying “you’re 2 cm”.

    Ultimately, while cervical exams and tracking dilation are likely to remain a standard part of labour care, it is simply interesting to know that the process is not as simple nor as straightforward as a door opening, or your skin stretching, from zero to ten centimetres over a consistent or predictable period of time. Labour is so much more individualized than that, and so much more fascinating. It is useful to understand more about what our bodies are actually doing when someone tells us we’re “6 cm dilated”, given that this means both so much, and so little, about our labour.

Stephanie Ondrack lives with her family, cats, and chickens in East Vancouver. 

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