How to Measure Purple Line for Dilation
While not all women will experience a purple line prior to giving birth, the majority do. You can gauge your level of dilation by measuring the length of any thin purple lines that appear. Even though you shouldn’t rely solely on this method and should always be aware of other signs of labor progress, it can be a very useful tool to have in your toolbox. Here’s how to measure purple line for dilation:
Know what to look for
The line will start at your anus and run upward toward the crest of your butt cheeks. As your labor progresses, the line should grow in length, moving further and further up your backside. It is wise to have one of your support people glance at your butt crack prior to labor beginning. It can also be helpful to take a photo of what your natal cleft normally looks like so it can be compared to how it looks during labor.
Ask for help
Given that you’re very pregnant, possibly uncomfortable, and the line is located in a difficult position to see on yourself, you’ll likely want to ask your partner, doula, or a medical professional for assistance.
Measure the line
Have your helper use a flexible measuring tape to measure the length of the line. It may help to bend over or position yourself on all fours. If you don’t have a flexible measuring tape available, you can use a piece of dental floss or string and then hold it against a ruler or standard measuring tape.
Calculate cervical dilation
Use a purple line dilation chart to turn your purple line measurement into an estimate of how dilated your cervix currently is. The length of the purple line at each stage of dilation can vary from person to person so purple line dilation charts provide overlapping estimates.
Please Note – This guide includes an extensive selection of purple line dilation pictures from real world birth journeys.
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 typically becomes apparent when the cervix is 3–4 cm dilated. But how in the world does that happen? Well, the purple line comes up from the edge of the anus as the baby descends into the deep pelvis. Vascular congestion at the base of the sacrum is thought to be the cause of this appearance. The purple line rises and the intra-pelvic pressure rises as the baby’s head decelerates. (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…