Estimating Cervix Dilation with the Purple Line
When you’re in or approaching labor, you may develop a purple line that runs vertically from your anus to the top of your natal cleft in between your butt cheeks. This “purple butt line,” as it’s often called, is said to first appear when the cervix is between zero and two centimeters dilated. Sometimes it is very faint while other it is quite bold, but it seems to be present in about 90% of labors.
This purple line may be the answer to one of the more difficult roadblocks people often face during labor: How to check for dilation in a way that’s comfortable.
Please Note - This guide includes an extensive selection of purple line dilation pictures from real world birth journeys.
Purple Line Theory: Transitioning From Pregnancy to Labor
The purple line theory is a simple method for self checking dilation that could be used by birthing people and their supporting people that is less intrusive than traditional cervical exams. The theory is based on observed data from midwives and physicians. Studies consistently show a medium-positive correlation between the appearance of this thin purple line and cervical dilation, as measured by traditional vaginal exams.
While more research will be conducted to determine the exact relationship between the purple butt line and the positioning of the fetal head, it seems to hold a lot of weight with medical professionals. Purple line theory is a valuable tool that birthing folks and their support teams can use in both home births and births in hospitals or other clinical settings.
How to Measure Purple Line for Dilation
While not everyone will develop a purple line before they go into labor, a majority of people do. If you develop a thin purple line, you can measure its length to get a general idea of how dilated you are. While you shouldn’t rely on this method alone, and should always pay attention to other signs of labor progression, it can be a great piece of knowledge to have in your toolkit. 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.
Using a Purple Line Dilation Chart
You and your midwife, doula, or other birthing-support team members can use the purple line dilation chart below to estimate how dilated you are. Keep in mind that the thin purple line is not a perfect measure of cervical dilation. The length of the purple line can vary by a centimeter or two between individuals, even at the same stage of dilation. That’s why there is some overlap in the chart.
3-6 cm Purple Line = 1-2 cm Dilated
When you’re just 1-2 centimeters dilated, the purple line should be approximately 3-6 cm long, beginning at your anus and running vertically up between your butt cheeks toward your lower back.
5-8 cm Purple Line = 3-6 cm Dilated
As you progress through the early stages of labor, the thin purple line begins to grow and lengthen along the butt crack. When you’re 3-6 centimeters dilated, the line is likely to be approximately 5-8 centimeters.
7-9 cm Purple Line = 7-8 cm Dilated
At the point where your cervix is 7-8 centimeters dilated, you can expect the purple butt line to be somewhere between 7-9 centimeters long. Keep in mind that the line may be very faint or bold, like it was drawn with a felt tip pen.
8-11 cm Purple Line = 9-10 cm Dilated
By the time you’re 9-10 centimeters dilated (which is considered full dilation and indicates the last stage of active labor), the thin purple line should be approximately 8-11 centimeters long.
Purple Line Dilation Image
The purple line can look different on different people, particularly in terms of visibility. In some cases, it can be very faint, while in others, it can be extremely visible. Generally, the purple line begins at the anus and extends through the crack to the top cleft of your butt cheeks. Sometimes the purple line dilation image is defined, and sometimes it can look more dispersed, like a bruise.
Purple Line Dilation Pictures
While it’s called “the purple line,” the color and appearance of this thin line can look quite different depending on the individual. In some cases, the line may appear red or brown and the appearance and clarity of the line can look different depending on the skin color and tone of the birthing person. The purple line dilation pictures on this page should give you some idea of what to look for.
Photo credit for the image at the top of this page goes to First Glance Photography.
What if I have a purple line but not in labor?
While the purple line is most common in people that are actively in labor, it can sometimes appear before that. The line is correlated with dilation, which can occur during active labor, or days or weeks earlier. Unfortunately, because there isn’t a perfect correlation between the purple line and how dilated you are, you won’t be able to tell for sure how close to labor you are. However, if you see the purple line but not in labor, it’s likely a sign that the labor process has begun or will begin fairly soon.
To learn more about purple line cervical dilation, speak to a Portland doula.
Doulas are a great resource when it comes to learning how to check purple line cervical dilation at home or while waiting to give birth in a clinical setting, whether you’re using a self exam or the purple dilation line method. Our Postpartum Doula Portland team are comprehensively trained on the physical, emotional, and psychological processes that take place during birth as well as everything from lactation supplements to reviews of the best online birthing classes. For compassionate and evidence-based information and support, get in touch with Wildwood Birth and speak with a Portland doula today.