Dilation and Effacement: What Does It Mean?

So you're in the office on your due date and your doctor checks your cervix and says it is "long and closed"...or you're 33 weeks and your cervix is already three centimeters dilated. You may wonder: what do those terms mean, and what do these findings mean to you and your baby?

First, definitions:

  • Dilation is how open the cervix is. Typically the cervix is closed through most of the pregnancy. It may open a little toward the end, and then during labor it makes its way from wherever it started, be it closed or four centimeters, to completely open, which is about ten centimeters (about the diameter of a softball, which is also about the size of a newborn's head).
  • Effacement is a trickier concept. The cervix has length to it, like the neck of a bottle. A long cervix is like the neck on a beer bottle. An "effaced" cervix is one that has lost some length and become more like the neck of a mayonnaise jar. A full-length cervix is between 3 and 5 centimeters long. Where does it go when it effaces? The cervix gets pulled up to become part of the lower uterus until all the cervix is gone; at that point the uterus really just has an opening at the bottom to let the baby out, and there's no longer any "bottle neck."

But what does it mean?

Near your due date, almost anything is "normal." You might walk around four centimeters dilated and 100% effaced, or your cervix might be long and closed. In general, with first babies you efface before you dilate much, and with subsequent babies you dilate first. Some dilation and effacement near term is usually good news: It takes several hours off of labor if you have already made some progress without labor contractions. Earlier in pregnancy, dilation and effacement can signal that the baby is going to come early. Ultrasound is sometimes used to measure the length of the cervix as a measure of the likelihood that the baby will be born before the due date.

If your doctor or midwife checks your cervix and tells you what he or she finds, ask what it means for you. Although obstetrics is not an exact science, sometimes findings on exam can help predict when you will give birth, how labor will go, and the likelihood of needing a cesarean.

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