Effacement and dilatation allow a baby to be born through the birth canal. Effacement means that the cervix stretches and gets thinner. Dilatation means that the cervix opens.
As labor nears, the cervix may start to thin or stretch (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 woman. In some women, the cervix may start to efface and dilate slowly over a period of weeks. But a first-time mother often will not dilate until active labor starts.
Late in your pregnancy, your health professional may check the cervix with his or her fingers to see how much it has effaced and dilated. He or she 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.
As the baby's head drops down into the pelvis, it pushes against the cervix. This causes the cervix to relax and thin out , or efface.
During pregnancy, your cervix has been closed and protected by a plug of mucus. When the cervix effaces, the mucus plug comes loose and passes out of the vagina. The mucus may be tinged with blood. Passing the mucus plug is called "show" or "bloody show." You may notice when the mucus plug passes. But you might not.
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.
After the cervix begins to efface, it will also start to open. This is called cervical dilatation.
Cervical dilatation 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.