Effacement is the term obstetricians use to describe certain changes in the cervix prior to childbirth. As delivery approaches, your baby will drop toward the cervix, or lower uterus. In response to this change in position, the walls of the cervix begin to efface, or thin out, to make room for the baby’s passage. 80 percent effacement in combination with advancing cervical dilation—or opening—is typically a sign that active labor and childbirth are close at hand.
During the latter stages of normal pregnancy, your baby will shift position inside your uterus, assuming a head-down profile in preparation for birth. When your body senses this positional change, it sends signals to temporarily alter the shape of the cervix. The order and speed of this cervical change varies from person to person. If you are a first-time mother, the process of effacement may begin some weeks before your due date, and will generally happen in advance of any sign of dilation. If you have given birth previously, dilation will typically happen prior to effacement.
First Stages of Effacement
When effacement begins, the changes in your cervical walls will loosen a protective plug of mucus that formed early in pregnancy. Passage of this mucus plug through the vagina, known as “show,” is your sign that cervical thinning is underway. In some cases blood is passed along with the mucus, leading to a condition called “bloody show.” Show is an easy way to mark the approach or onset of labor, but it is also easy to miss. However, do not worry if it passes unnoticed. While it is a helpful marker of events, missing it carries no medical consequences.
The Progression of Labor
At some point in early first stage labor, you will begin to experience effacement and dilation simultaneously. These cervical changes will be accompanied and accelerated by contractions in the uterus, and it is the combination of these three factors that will determine the overall timing and progress of labor.
The progression of labor is notoriously impossible to judge, but changes in cervical effacement and dilation—combined with the length and severity of contractions—provide some rough guidelines to the status of your impending delivery. Effacement is measured as a percentage of the thickness of the cervical wall, while dilation is measured in centimeters of openness. Early on, effacement may be 10 percent, while dilation may be zero to one centimeter. As first stage labor develops, effacement and dilation will advance in irregular increments.
Effacement, Dilation and Active Labor
Your main cue of advancing early stage labor will be a shortening of time between contractions. When your contractions last a minute or longer—and come every two or three minutes—you are nearing or entering active labor and should proceed to the location you have arranged for birthing. Medical personnel will then monitor your effacement and dilation. Typically, when your cervix has effaced 80 percent and dilated four centimeters, you may expect an acceleration of active labor leading to the birth of your child.