What is dilation and effacement? Your cervix begins to dilate (open) during the last phase of pregnancy, and when you are in labor. Dilation (deye-LAY-shun) of the cervix is measured in centimeters from zero to 10. Your cervix is fully open when it is dilated to 10 centimeters. The cervix is normally about one and one-half inches thick. Your cervix thins and softens as it gets ready for birth. Effacement (e-FAYS-ment) of the cervix is measured in percents. Your cervix is half of its original thickness when it is 50 percent effaced. It is completely thinned out when it is 100 percent effaced. This means that when you are dilated to 10 centimeters and effaced to 100 percent, you can start pushing. Some moms can get to complete and not be able to deliver vaginally. They may need a cesarean section.