An effaced cervix is one that has thinned and shortened in preparation for vaginal childbirth. During most of pregnancy, the cervix is firm and thick, acting as a closed barrier between the uterus and the birth canal. As your body prepares for delivery, the cervix gradually softens, thins out, and eventually merges with the lower part of the uterus so your baby can pass through.
Effacement is measured in percentages. At 0% effaced, your cervix is still its full length and firmness. At 100% effaced, it has thinned completely. Both full effacement and full dilation (10 cm) need to happen before the pushing stage of labor can begin.
What Happens Inside the Cervix
The cervix is mostly made of connective tissue, particularly collagen and elastin fibers. In the final days of pregnancy, a process called cervical ripening breaks down those fibers through a series of biochemical changes. Fluid flows into the tissue, and a localized inflammatory response develops. The net result is that the cervix transforms from a closed, rigid structure into something soft and stretchy.
Think of it like a thick turtleneck being pulled and stretched until it’s paper-thin. The cervix doesn’t disappear; it simply thins so much that it becomes part of the lower uterine wall, creating a smooth path for delivery.
How Effacement Is Measured
Your provider checks effacement during a cervical exam, usually in the final weeks of pregnancy or during labor. They estimate the thickness of the cervix by feel and assign a percentage:
- 0%: The cervix is long, thick, and firm. No thinning has started.
- 50%: The cervix has thinned to about half its original thickness.
- 80% or higher: The cervix is significantly thinned and labor is typically progressing well.
- 100%: The cervix is completely thinned out and ready for delivery (along with full dilation).
These percentages are an estimate, not a precise measurement. Two providers examining the same cervix might give slightly different numbers. What matters most is the trend over time.
Effacement vs. Dilation
Effacement and dilation are related but distinct processes. Effacement is the thinning of the entire cervix. Dilation is the opening of the cervical os, the part of the cervix that faces the vagina. Dilation is measured in centimeters, from 0 (completely closed) to 10 (fully open).
The order these happen in depends largely on whether you’ve given birth before. In a first pregnancy, the cervix typically effaces first, then dilates. In second or third pregnancies, effacement and dilation often happen at the same time. It’s also possible to be dilated a few centimeters without much effacement, which is more common in people who have previously delivered vaginally.
What You Might Feel
Early effacement often happens without any obvious symptoms. Many people are surprised to learn at a routine late-pregnancy appointment that their cervix is already 50% or 60% effaced. You can’t reliably tell from the outside how effaced you are.
That said, some signs can hint that your cervix is changing. As the cervix thins, the mucus plug that sealed it during pregnancy may loosen and come out as a thick, sometimes blood-tinged discharge (often called “bloody show”). You may also notice increased pelvic pressure or a feeling that the baby has “dropped” lower into your pelvis. Irregular contractions, sometimes called Braxton Hicks, can become more frequent as the cervix softens and thins.
None of these signs tell you exactly how effaced you are, and none of them mean labor is imminent. Effacement can progress slowly over weeks or quickly over hours.
What Your Effacement Percentage Means for Labor
Being partially effaced at a prenatal visit is a sign your body is preparing, but it doesn’t predict when labor will start. Some people walk around at 70% effaced for weeks before labor begins. Others go from minimal effacement to fully effaced in a matter of hours once active labor kicks in.
When providers assess how ready your body is for labor or induction, effacement is one of several factors they consider together, alongside dilation, the baby’s position, and how soft the cervix feels. Higher effacement generally means labor is more likely to progress smoothly if it starts on its own or is induced. A cervix that is 80% or more effaced is considered quite favorable.
The key number to remember: your cervix needs to reach 100% effacement and 10 cm dilation before it’s time to push. These two milestones work together. A cervix that is fully effaced but only a few centimeters dilated still has more work to do, and vice versa.
First Pregnancy vs. Subsequent Pregnancies
If this is your first baby, expect effacement to be the first measurable change. Your cervix will thin out significantly before it starts to open. This process can begin days or even weeks before labor, which is why a provider might tell you at 37 or 38 weeks that you’re already partially effaced even though contractions haven’t started.
In later pregnancies, the cervix has already stretched once before. It tends to be softer and more responsive, so effacement and dilation often progress simultaneously rather than in sequence. This is one reason second and third labors are frequently shorter: the cervix doesn’t need as much time to go through each step individually.