Overview
Effacement and dilation allow a baby to be born through the birth canal. Effacement means that the cervix stretches and gets thinner. Dilation means that the cervix opens.
As labor nears, the cervix may start to thin (efface) and open (dilate). This prepares the cervix for the baby to pass through the birth canal (vagina). How fast the cervix thins and opens varies for each person. In some cases, the cervix may start to efface and dilate slowly over a period of weeks. But someone giving birth for the first time often won't dilate until labor starts.
Late in your pregnancy, your health professional may check your cervix with their fingers to see how much it has effaced and dilated. They will wear sterile gloves to do this.
During labor, contractions in your uterus open (dilate) your cervix. They also help move the baby into position to be born.
During pregnancy, your cervix has been closed and protected by a plug of mucus. When the cervix effaces and dilates, the mucus plug comes loose and passes out of the vagina. The mucus may be tinged with blood. You may notice when the mucus plug passes. But you might not.
Effacement
As the baby's head drops down into your pelvis, it pushes against the cervix. This causes the cervix to stretch and thin out, or efface.
Effacement is described as a percentage. For example, if your cervix is not effaced at all, it is 0% effaced. If the cervix has completely thinned, it is 100% effaced.
Dilation
After your cervix starts to efface, it will also start to open. This is called cervical dilation.
Cervical dilation is described in centimeters from 0 to 10. At 0, the cervix is closed. At 10, it's completely dilated. Your cervix must be completely dilated before you can start the pushing stage.