Dilation and effacement refer to the condition of the cervix during pregnancy and labor. Dilation refers to the opening of the cervix, while effacement refers to the "ripening" (thinning and softening) of the cervix.
Dilation is measured in centimeters, from 0 to 10. Your cervix is fully open and you should be able to push when it is dilated to 10 centimeters. Occasionally, a physician will measure dilation in "fingers." Dilation often begins days or weeks before labor actually begins. At first, the progress may be very slow. Some women may be dilated 2 to 3 centimeters long before labor. Once active labor begins, you will begin to dilate more quickly.
Your cervix prepares for birth by softening and thinning. You won’t feel this happening; it may only be measure with a vaginal exam. Effacement is measured in percent. When your cervix is normal, it is considered to be 0% effaced. When you’re 50% effaced, your cervix is half its original thickness. When your cervix is 100% effaced it is completely thinned out and you are ready for vaginal delivery.
A measurement called the "Bishop’s Score" is sometimes used to determine the chance of a successful vaginal delivery, or whether a woman may require a cesarean section. The Bishop’s Score considers dilation and effacement, as well as other characteristics including station of the fetus, position of the cervix and consistency of the cervix.