Effacement is a physiological change the cervix undergoes to prepare for childbirth. This process involves the thinning and shortening of the cervix, which acts as the gateway between the uterus and the vagina. Healthcare providers track this change, along with cervical dilation, as two primary measurements during late pregnancy and active labor. Both changes must be complete before a baby can safely move through the birth canal.
What Effacement Physically Means
Before effacement begins, the cervix is firm, long, and thick, often measuring three to four centimeters in length. This structure keeps the pregnancy securely contained within the uterus until the body is ready for labor. Effacement, sometimes called cervical ripening, is the biological process where the cervix softens, shortens, and begins to thin.
This physical transformation occurs as the lower part of the uterus begins to pull the cervix upward. Uterine contractions, even mild ones before active labor, help draw the cervical tissue up into the uterine wall. The resulting change is similar to how a turtleneck sweater collar might be rolled up, transforming a long, narrow tube into a flat, thin edge.
The thinning is necessary because the cervix’s normal thickness would obstruct the baby’s passage. As the baby’s head descends into the pelvis, it applies pressure that encourages the cervix to stretch and thin. This shortening and softening is a fundamental step in making the birth canal wide enough for the baby.
How Effacement is Measured
Healthcare providers measure cervical effacement using a percentage scale, which estimates how much the cervix has thinned compared to its original length. A measurement of 0% effaced means the cervix is still at its full, un-thinned length and thickness. Conversely, 100% effacement indicates that the cervix has completely thinned out, becoming paper-thin.
This measurement is obtained through a manual cervical examination, where a provider uses gloved fingers to feel the thickness and length of the cervix. If the cervix is measured at 50% effaced, the tissue has shortened and thinned to half of its normal pre-labor length. Moving from 50% to 100% signifies continuous progress in the thinning process.
Achieving 100% effacement is required for a vaginal delivery. The measurement is an estimate based on the provider’s assessment, but it serves as a reliable indicator of how prepared the cervix is for the next stage of labor. The percentage scale provides a standardized way to track this progress throughout late pregnancy and labor.
Effacement and Dilation: The Full Picture of Labor Progress
Effacement is one half of the process known as cervical ripening, while the other half is dilation. Dilation refers to the widening or opening of the cervical entrance, which is measured in centimeters, ranging from 0 cm (closed) to 10 cm (fully open). Effacement is about the cervix getting thinner, measured in percentages, and dilation is about the cervix getting wider, measured in centimeters.
These two processes often work together, but their timing can vary, especially between pregnancies. For a person delivering a first baby, effacement often occurs entirely or mostly before significant dilation begins. However, in subsequent pregnancies, the cervix may dilate a few centimeters before it is fully effaced.
During a cervical check, a healthcare provider assesses both measurements simultaneously to determine the status of labor progression. Active labor is typically defined by a combination of regular contractions and progressive changes in both effacement and dilation. The cervix must be 100% effaced and 10 centimeters dilated to be considered ready for the second stage of labor, which involves pushing the baby out.