Cervical effacement refers to a thinning of the cervix. It can be expressed as a percentage. Prior to effacement, the cervix is like a long bottleneck, usually about four centimeters in length.This prepares the cervix for the baby to pass through the birth canal. It also help move the baby into position to be born. The cervix starts out three to four centimeters long. When it is 50 percent effaced, it is about two centimeters long. When it is 100 percent effaced, it is "paper-thin." By: https://www.instagram.com/p/CT6XJU6MOEH/?utm_medium=copy_link