The Purple Line of Labor progression: Myth or Magic?
Updated Oct.14, 2022
Say What?
Have you ever heard of this? Have you seen it?
Did you know that the Purple Line is seen in about 76% of active laboring women and can be used for estimating progression of labor and station of baby? Really! How crazy is that! It is more readily seen in women who are of white ethnicity and who have experience a premature rupture of membranes (1). It usually becomes visible when the cervix is dilated to 3-4 cm. But how in the world does that work? Well, as the baby descends into the deep pelvis, the purple line rises up from the outskirts of the anus. This appearance has been thought to occur because of the vascular congestion at the base of the sacrum. As baby’s head descends, the intra-pelvic pressure increases and the purple line rises.(2)
As a doula, I don’t do internal exams. Ever. But fortunately, Mother Nature helps me out by giving a bunch of clues about progression of labor: vaginal discharge, contraction pattern and intensity, vocalization changes, pelvic floor pressure, changes in demeanor to shakes / chills, and…
The Purple Line
So, just where is this purple line to be found? Back in my midwifery days, we called it the “Natal Cleft”, but most folks just call it the “butt crack”! Natal Cleft sounds more like something exciting is about to happen, doesn't it? I kind of like that!
As a doula, I want to know 2 things about the labor that I am attending:
Position of the Baby and Station of the Baby.
Yep, I am really not as interested in dilation. Dilation is great, but Birth Professionals know that dilation is only one indication of progression and, in fact, is not always that reliable for how soon baby is to being born. We have all seen those moms who take 12 hours to dilate to 4 cm and then 1 hour to “fully” dilate to 10cm. We have also had moms who took 1 hour to dilate to 7cm and then another 12 hours to fully dilated. What the heck, right?
The cool thing is that there is actually a positive correlation between the purple line and the station of the baby’s head (3). So, it’s helpful to us to have an idea of: WHERE IS THE BABY?
It’s not about Dilation…
It’s about Station
Known as a somewhat imprecise assessment of dilation (48-56% accurate according to Shepherd et al, 2010 and finding differ in different studies), cervical assessment by internal exam by 2 different providers can widely differ, too. Have you ever experienced that? The nurse checks you and she says you are 8 cm and the next nurse checks and says that you are 6 cm… Frustrating, no?
Reduce infection risk and keep your birth focus
One of the advantages of using The Purple Line is that it is completely non-invasive. This important because there is a correlation between the number of internal exams and increased risk of infection. If your “waters” have already released, this can be particularly important to remember. But one of the big benefits to the birthing person, is that she does not have to interrupt her birth focus, “roll over and get checked”. In fact, she doesn’t need to even be aware of the line is being noted, which really helps her stay in her inner relaxation focus.
If you are pregnant, ask your partner or your doula to take pictures of your natal cleft along the way. No kidding! It may be an interesting experiment and fun to see if you can guess before the care provider tells you what they think the dilation and “station” are.
Sources:
Nunes, R. D., Locatelli, P., & Traebert, J. (2018). Use of the purple line to diagnose cervical dilatation and fetal head station during labor.
Farrag¹, R. E., & Eltohamy, N. A. E. (2021). Accuracy of purple line to monitor labour progress: Longitudinal study.
Irani, M., Kordi, M., & Esmaily, H. (2018). Relationship between length and width of the purple line and foetal head descent in active phase of labour. Journal of Obstetrics and Gynaecology, 38(1), 10-15.
Irani, M., Kordi, M., & Esmaeili, H. (2022). Purple line Alteration in prediction of labor progress. The Iranian Journal of Obstetrics, Gynecology and Infertility, 24(13), 51-58.
Shepherd, A., Cheyne, H., Kennedy, S., McIntosh, C., Styles, M., & Niven, C. (2010). The purple line as a measure of labourprogress: a longitudinal study. BMC pregnancy and childbirth, 10(1), 1-7.