• Rosemary Joyce

What on earth is 'the purple line'?!

Updated: Aug 7, 2018

Is vaginal examination the only way to measure dilation in labour? Or is it true that one could tell how dilated a labouring woman is, just by, well… looking at her behind?!

While vaginal examinations are able to give the care provider more information than just dilation, they do come with risk, are only accurate 50% of the time, and cause many women pain, embarrassment, disappointment. They can also be a source of trauma to a sexual abuse survivor.

Here's where the purple line becomes useful!

Research shows 76% of women develop a purple line during labour -starting at the anus and rising up between the buttocks as labour progresses. This means that as the Mama is dilating and baby's head is descending, the length of the purple line is growing!

No one is certain why the purple line occurs, but it is thought to be linked to an increase in blood supply at the bottom of Mama's sacrum during labour.

(Photo credit: Science & Sensibility)

Research also shows...

  • Women who are having a spontaneous labour are much more likely to have a purple line (80%).

  • Women having an indication are less likely to have a purple line (59%).

  • The purple line is just as accurate in a first time Mama, as it is in a Mama who has given birth before

As with all decisions in birth, whether or not you choose to have a vaginal examination and/or use the purple line as a guide is your choice. The reality is that dilation is not an accurate predictor of how much longer labour will be. However, the purple line may be a source of encouragement for some parents if they find out things are moving forward, without interrupting the flow of labour.


Shepherd, A., Cheyne, H., Kennedy, S., McIntosh, C., Styles, M., & Niven, C. (2010). The purple line as a measure of labour progress: a longitudinal study. BMC Pregnancy and Childbirth, 10: 54. Doi 10.1186/1471-2393-10-54

Cockeram, M. (2014). The red/purple line: An alternate method for assessing cervical dilation using visual cues. Retrieved from https://www.scienceandsensibility.org/blog/the-red/purple-line-an-alternate-method-for-assessing-cervical-dilation-using-visual-cues


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