The term erased it is most often used to describe the process the cervix goes through to prepare for childbirth. The cervix is located at the bottom of the uterus, where it extends into the vagina. Normally, the cervix is in the shape of a small, squat cylinder with a central opening that remains closed most of the time. During menstruation, the cervix opens slightly, called dilation, to allow menstrual fluid to pass through. Effacement of the cervix means that it flattens and thins to allow further dilation before delivery so that the fetus can pass into the vaginal canal.
Removal of the cervix is a gradual process. Towards the end of pregnancy, many women experience Braxton Hicks contractions. These contractions are sometimes called false labor, but they are thought to be a component of effacement. Usually painless and sometimes unnoticeable, Braxton Hicks contractions cause the uterus to tighten for a few minutes at a time. The contractions, in turn, activate the cervix to begin the thinning process.
Before effacement, when the cervix is thick and tight, it is considered effaced at 0%. When the fetus is ready to pass through the vaginal canal, the cervix is paper-thin and 100% effaced. The portion of the cervix that extends into the vagina is usually about 1.5 to 1.5 inches (2.54 to 3.8 cm). Thus, when the cervix is 50% effaced, it has shortened and thinned to approximately 0.5 - 0.75 inches (1.3 - 1.9 cm). This is measured throughout the first stage of labor through periodic examinations. As effacement progresses, so does dilation, which occurs during the first stage. Once both effacement and dilation are at 100%, the second stage of labor begins and the woman begins to push.
Sometimes women reach the end of pregnancy without the cervix showing signs of effacement. In this case, a doctor may recommend a vaginal suppository or other treatment to encourage the cervix to soften. This triggers effacement and dilation. However, this type of procedure is generally reserved for women who are considered backwards. It's always best to let labor happen naturally, but if a woman goes beyond what is considered the appropriate gestational period, doctors can begin to induce pregnancy by first softening the cervix. Most doctors don't consider a fetus to be late until the 40th week of pregnancy.