Cervical effacement refers to the thinning and shortening of the cervix in preparation for childbirth. It is expressed as a percentage, indicating how much the cervix has thinned from its normal thickness to almost paper-thin. This process facilitates the passage of the fetus through the birth canal. Effacement precedes or occurs simultaneously with cervical dilation, which is the opening of the cervix. Unlike dilation, which describes the widening of the cervical opening, effacement specifically describes the softening and thinning of the cervical tissue. Recognizing effacement is crucial for assessing labor progression.

Reference: Williams Obstetrics, Cunningham F.G., 25th Edition.