cervical effacement

The cervix stretches and gets thinner.

During pregnancy, the cervix has been closed and protected by a mucus plug. 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 bloody show."

As the baby's head drops down into the pelvis, it pushes against the cervix, causing the cervix to relax and thin out, or efface.
It is described as a percentage.
• Not effaced at all: 0% effaced.
• Completely thinned: 100% effaced.

After the cervix begins to efface, it will also start to open (cervical dilation).
(Comparison)
Effacement: The cervix stretches and gets thinner.
Dilation: The cervix opens.