Effacement is the thinning and shortening of your cervix as your body prepares for vaginal delivery. Your cervix starts out thick and firm, roughly like a tube a few centimeters long. As labor approaches, it gradually thins until it becomes a paper-thin band. Providers measure effacement as a percentage from 0% (no thinning) to 100% (completely thinned out), and your cervix needs to reach 100% effaced and 10 cm dilated before vaginal birth can happen.
How Effacement Works in Your Body
For most of pregnancy, your cervix acts as a sealed, firm barrier between your uterus and vagina. It gets that firmness from tightly bundled collagen fibers held together by chemical bridges. In late pregnancy, your body starts breaking down those bridges through a process that resembles inflammation. Water molecules move in between the loosened collagen fibers, making the tissue softer and more pliable.
Once contractions begin, the softened cervix gets pulled upward and over the baby’s head. Think of it like a turtleneck sweater being stretched wide as you pull it on. The tissue fibers actually reorient in the direction of the force, and the cervix has a built-in ratchet-like quality: once it stretches open during a contraction, it stays at that wider point rather than snapping back. This is why labor progresses forward rather than resetting between contractions.
How Effacement Is Measured
During a cervical check, your provider inserts two gloved fingers and feels the thickness of your cervix. In early labor, it feels like a thick tube. As effacement progresses, that tube shortens until eventually the cervix is just a thin ring around the provider’s fingers, which means you’re fully effaced. This is a hands-on estimate, not a precise measurement, so you might hear slightly different numbers from different providers.
Effacement is also part of a scoring system called the Bishop score, which helps providers gauge how ready your body is for labor. The score assigns higher points as effacement increases: 0 to 30% effaced earns 0 points, 40 to 50% earns 1 point, 60 to 70% earns 2 points, and 80% or more earns 3 points. A higher total score means your cervix is more “ripe” and labor is more likely to progress on its own or respond well to induction.
Effacement vs. Dilation
Effacement and dilation are two separate changes happening to the same structure. Effacement refers to the cervix getting thinner and shorter. Dilation refers to the cervical opening getting wider, measured in centimeters from 0 (closed) to 10 (fully open). They usually happen together during active labor, but they don’t always progress at the same pace.
The pattern depends partly on whether you’ve given birth before. If this is your first baby, your cervix will typically efface first, thinning out significantly before it starts to open. If you’ve had a previous vaginal delivery, you may dilate several centimeters before much effacement has occurred. Some people efface and dilate at roughly the same rate. None of these patterns is better or worse. They’re just different routes to the same destination.
What Effacement Feels Like
You can’t directly feel your cervix thinning. There’s no specific sensation that tells you, “I’m now 50% effaced.” What you may notice are indirect signs. Increased pelvic pressure as the baby drops lower is common in the weeks before labor. Some people lose their mucus plug, a thick discharge that sealed the cervical opening during pregnancy, as the cervix begins to thin and open. You may also notice irregular contractions (Braxton Hicks) that can contribute to early effacement without signaling active labor.
The only reliable way to know your effacement percentage is through a cervical exam. And a single number on its own doesn’t predict exactly when labor will start. Some people walk around 80% effaced for weeks. Others go from thick to fully effaced in a matter of hours once active labor kicks in.
When Effacement Happens Too Early
Effacement before 37 weeks raises concerns about preterm labor. One way providers monitor this is by measuring cervical length on ultrasound, which gives a more precise picture than a manual exam. A cervix shorter than 25 mm (about 1 inch) in the second trimester is generally considered short, and the risk of preterm birth rises substantially as length decreases. Women with a cervical length under 15 mm at 22 to 24 weeks account for the vast majority of very early preterm births, those before 28 weeks.
If your provider finds that your cervix is shortening too early, treatments may include progesterone supplements to help maintain the cervical tissue, or in some cases a cerclage, which is a stitch placed around the cervix to help keep it closed. Routine cervical length screening is most commonly offered to people with a history of preterm birth, though practices vary.
What Your Effacement Percentage Actually Tells You
When your provider says you’re 50% effaced at a late-pregnancy appointment, it means your body is making progress toward labor, but it doesn’t come with a countdown clock. Effacement is one piece of a larger picture that includes dilation, the baby’s position, and contraction patterns. Being significantly effaced at 38 or 39 weeks is encouraging, but plenty of people stay partially effaced for weeks without going into labor.
Where effacement becomes more meaningful is during active labor. Once you’re in the hospital and being checked regularly, the rate of change matters more than any single number. Steady progression from, say, 60% to 80% to fully effaced over several hours, alongside increasing dilation, tells your care team that labor is moving forward as expected. Stalled effacement and dilation over many hours, despite strong contractions, is one of the factors that might lead to a conversation about other options.