So we all know how our cervix works in labour, right? You have some contractions, it opens about a centimetre every hour and when it gets to ten centimetres, you push your baby out.
Well, sort of. Like most things to do with the human body, the text books only tell part of the story. The range of normal for human bodies can be quite broad – think about the menstrual cycle. We assume that a normal cycle is 28 days long. Yet we also know that for some women, their cycle is 30 days. Or even 35 days. And for those women, that cycle length is perfectly normal. The human body generally has a range of values that define normal, rather than a single specific value, and this is true of what our cervix is doing in labour, too.

Here are five things you should know about your cervix before labour begins.

1. Your cervix probably won’t dilate at a consistent, predictable rate.

The idea that the cervix should dilate at 1cm per hour from the onset of active labour comes from a 1955 study by Dr E Friedman, who studied the labours of five hundred first time mothers and plotted their rate of dilation on a graph. As was the way of things at the time, the average age of mothers in the study was 20 years old, and a full 96% of these mothers were sedated during labour. (In contrast, the average age of first time mothers in 2015 is 31 years, and we don’t sedate women in labour any more). The issues with this study are many and well documented, but it was widely accepted as standard maternity care for many years. Some care providers still use it to assess progress in labour.
We know now that many women will dilate slowly in early labour, and dilation will speed up once they reach about 6cm. This observation is now so common and borne out by current research, that the governing body of US obstetricians has updated its guidelines to reflect a 6cm starting point for active labour (until recently, active labour was deemed to begin at 4cm). Incidentally, I’d expect a similar revision in Australia shortly. Some women will dilate 1cm every two or three hours from start to finish. Others will dilate at 2cm an hour from the very beginning. And there will be others still, who dilate in fits and starts – and that’s just how they do things thank-you-very-much. The variation around what is normal is huge.

Which is why many care providers now focus on progress. So while a woman might not be dilating at one centimetre an hour, she’s still showing signs of progress and her baby is coping with labour well.

2. Your cervix moves from back to front as well dilating.

During pregnancy, the opening of your cervix points back towards your bottom. As labour gets closer it begins to move to a more central position, before finally coming right forward to the front. If you have a vaginal exam prior to labour you might be really discouraged to be told you’re not dilated at all –  but ask about the position of your cervix, and you may be pleasantly surprised. This change in position is a positive sign that your body is doing what it should.

3. Your cervix is the queen of multi-tasking.

As well as opening, your cervix also needs to thin, or efface to let your baby be born. For first time mothers, this thinning out often occurs in the early phase of labour. Once the cervix has thinned, or almost thinned, it will then begin to dilate. This is one reason for the stories about the eager first time mum experiencing regular contractions for a number of hours, expecting to be admitted when she arrives at hospital. There, she’s told she’s nice and thin and about a centimetre dilated…and sent home again. Or even worse, she’s told she’s not in labour yet because she’s less than four centimetres – the point caregivers consider active labour to begin. To say this is demoralising after many hours of regular contractions would be a drastic understatement; it can completely derail a woman’s focus and positivity. But it’s important to focus on the fact that the contractions of early labour are doing something – they’re not wasted. Effacement is a step in the process.

Have you ever wondered why experienced mums often birth much more quickly? Generally, their cervix will thin out and open at the same time. They’ll also usually begin labour with some effacement and dilation well underway.

4. Your cervix isnt a crystal ball.

Vaginal examinations may play a role in your labour, but it’s not to tell you how much longer you have to go. Providers do VEs for lots of reasons; to confirm you’re making progress, to check the position and angle of the baby’s head, and to determine how low your baby is in your pelvis. They don’t do them to gauge how long until your baby is born, and the best you can hope for here is an educated guess. Try to avoid doing what I call “labour maths”. This is when you or your partner start running mental calculations about how long it’s taken to reach a given point of dilation, and projecting forwards to work out when your baby will be born. Labour doesn’t work like that, see point 1.

5. 10 Centimeters is a ballpark.

Your cervix will dilate only as far as it needs to for your baby’s head to move through it. If your baby is small or preterm, it may only need to dilate to 9cm before she can come through. If your baby is on the big side, it may need to dilate a little more. In addition, vaginal examinations are an art rather than a science. They’re done by feel; the care provider can’t actually see your cervix and they’re using their fingers to measure it, not measuring instruments. This is why two care providers can examine the same woman and have different assessments of how dilated she is.
Going into labour believing that your cervix must behave a certain way can really mess with your head. Your body is unique and your process will unfold in a unique way. Keep communicating with your caregiver about any concerns, but as long as you and your baby are healthy and things are changing, know that your body is doing what it needs to for your baby to be born.


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