The Purple Line – Find Out If You Are Dilating

by | PREGNANCY

There is no doubt that the most reliable way to tell, if you are dilating and also how much you are dilated is a vaginal exam. However, a vaginal exam is neither a very pleasant experience nor always an option.

Luckily, the body itself has found its own ways to tell you if you are dilating (it even gives you a ROUGH IDEA about how much you are dilated). You just need to know where to look and how to interpret what you see!

One of the most remarkable ways in which our body tells you that you are dilating is the so-called Purple Line! It is a purple or brownish line (mostly depending on skin color) that extends from a woman’s anus upwards to the top of the cleft between her buttocks!

To be precise, it does not appear in all women! According to research, it appears in about 76% of all women when they are dilating (1).

However, from my personal experience, I very much doubt that 76% of women develop a purple line.

I’d rather say that 76% of women do NOT develop a purple line. But this may be a question of ethnicity.

So, what does the purple line mean?

But before we start: if you’d rather watch a video about this, scroll to the bottom of the page!

What Exactly is the Purple Line?

The following graph is an illustration of the purple line and where exactly it can be found:

Now, according to research (1), if a woman has a purple line, it is likely that she is dilating.

Of course, as always when it comes to scientific studies, it is difficult to say if the findings apply to EVERY woman in this world.

However, so far, we only had 4 cases of women who were not dilated although they had a purple line.

Given that the purple line is visible in your case, then you would see it close to your anus first and then extending upwards to the top of the cleft between your buttocks. In the final stage, the purple line will usually be approximately 10 cm in length.

Scientists are still indifferent, as to why a woman’s body may develop a purple line. However, what they did find is that there seems to be a medium positive correlation between the length of the purple line and the cervical dilation.

What this means is that we can get a VERY ROUGH idea about how much a woman is dilated, based on the length of her purple line.

In fact, one clinical study came up with the following table which shows the average length of the purple line of the woman in that study given their cervical dilation (1). The numbers in brackets are the standard deviations.

 

Cervical Dilation Mean Length of Purple Line (SD)
1-2 cm 5.3 cm (3.1 cm)
3-4 cm 7.8 cm (3.4 cm)
5-6 cm 7.8 cm (2.4 cm)
7-8 cm 8.7 cm (2.2 cm)
9-10 cm 9.6 cm (2.1 cm)

How to Interpret the Length of the Purple Line

As already mentioned, the two numbers, length of purple line and cervical dilation, are not perfectly correlated. Therefore, we cannot say that if a woman’s purple line is, say, 1cm long, her cervix is 1cm dilated.

Instead, as we can see from the table above, the purple line may be as long as 5.3 cm, when a woman is only just 1-2 cm dilated.

BUT: here is the problem: the average numbers that you can see in the table avove are indeed just average numbers across all 109 women of that study who developed the line.

The numbers in the brackets, on the other hand, are the so-called standard deviations. These numbers tell us how much, on average, the length of the purple line – that was measured during the study – deviated from the average value. And as we can see, the standard deviations are quite high.

So for example: at a dilation of 1-2 cm, the purple line was 5.3 cm on average across all 109 women. However, the standard deviation was 3.1 cm and thus very high compared to the average value.

What this means is that, at a dilation of 1-2 cm, the length of the purple line of the women of the study, was not necessarily close to 5.3 cm (although, again, that’s the average number).

Instead, some women may have had a purple line of 2.2 cm, some may have had a purple line of 3.1 cm, some may have had a purple line of 7 cm, and others may have had a purple line of 6.4 cm etc., when their cervix was about 1-2 cm dilated.

In other words, it is very difficult to conclude from the length of the purple line how much a woman is dilated.

Nevertheless, at least, we see a trend. And that trend tells us that the longer the length of the purple line, the more the cervix seems to have dilated. Therefore, we get at least a VERY ROUGH idea about how much the cervix has dilated, when we know the length of the purple line.

So, How can You Tell How Much You Are Dilated?

Well, of course, the most reliable method is definitely to have a vaginal exam. But as already mentioned that’s not always a viable option.

An alternative approach is to take into account another approach, not just the Purple Line alone, to estimate how much you are dilated.

For that purpose, some midwives make use of the Fundus Theory. Just keep in mind that the Fundus Theory can only be applied when you are in active or transitional labor.

But to be very clear, the Fundus Theory is not science based atll, so we don’t know how accurate it is for the general public. However, we know that it was pretty accurate in many women that we personally know when they were dilating (including in our own case).

The reason why we mention the Purple Line approach together with the Fundus Theory is because if looked at them separately, both, the Purple Line and the Fundus Theory alone may not be a great help if you cannot confirm the number (how much you are dilated) somehow.

However, when you look at the combined information that BOTH approaches tell you, that’s when you may get closer to the actual number how much you are dilated.

If you want to know more about the Fundus Theory, check out the following video in which we explain both, the Purple Line and the Fundus Theory:

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Sources

Shepherd, S. Cheyne, H. et al. (2010): The purple line as a measure of labour progress: a longitudinal study. In: BMC Pregnancy Childbirth. Sep 16; 10:54. doi: 10.1186/1471-2393-10-54. https://pubmed.ncbi.nlm.nih.gov/20846387/

Medical Disclaimer: The information on this page is not intended to diagnose, prevent, mitigate, treat or cure any disease! It is not personal medical advice. We recommend that you ask a doctor whenver you are looking for medical advice!

ABOUT THE AUTHOR

Nathalie Kaufmann & Mathias Ritter

Nathalie is a pregnancy and birth Consultant and a TCM Therapist with almost 20 years of experience in Traditional Chinese Medicine (TCM), acupuncture, reflexology, Shonishin baby massage techniques, Western and Eastern massage techniques (including TUINA), as well as herbal medicine and nutrition.

She has worked in hospitals across London and was Head of the Maternity Acupuncture Clinic at the Whittington hospital in London. Today, Nathalie runs her own company and helps pregnant women with pregnancy- and birth-related issues. She also specializes in alternative treatments for babies and children.

Mathias is a Researcher and Science Geek who holds two Master of Science degrees. He has been involved in several health-related businesses over the past 10 years and has held presentations about health-related topics across Europe. He specializes in research regarding pregnancy-, birth and baby-related topics.

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