We’ve covered dilation, but is that all there is to it? Of course, the answer is no. Why else would I be writing this post, right?? Now we need to talk about the next measure — effacement.
Dilation is actually not always the most important measure of labor progress, though it might be the only number you ever really hear. Effacement tells you more, especially in early labor.
So what is effacement?
Cervical effacement is the thinning of the cervix. Remember that the cervix is the bottom portion of the uterus and that as the uterus contracts over time, it pulls back the cervix and muscle relocates to the fundus to help with power to push the baby out. The more it pulls back, the thinner the cervical area becomes.
The cervix starts approximately 2-3 cm thick and progresses to the point that it is paper thin. In fact, sometimes providers might think a cervix is completely dilated when it is actually not very dilated at all, but the cervix has become so thin it is hard to feel and thus it is mistaken for being completely dilated.
Many moms are discouraged when they hear their dilation and think they haven’t progressed very far. They sometimes feel like their contractions aren’t doing anything. However, it is possible their effacement is well advanced.
Often times effacement happens first and then dilation progresses rapidly afterward. A large portion of early labor is commonly spent effacing the cervix, not necessarily dilating it. Once “active labor” starts, often all that’s left to do is dilate because all those seemingly endless contractions of early labor have completely thinned out the cervix. That is one reason why things really seem to get moving once this long-awaited period of active labor finally begins. The baby’s head moves down, the remaining thinned-out cervix pulls back over the head, and before you know it, birth is imminent.
As mentioned regarding dilation, the full measure of labor progress is expressed with a series of 3 measures:
dilation (# of cm) / effacement (%) / station (+/-)
So effacement is the middle number. If you’ve ever heard a provider say something like, “She’s 3, 50, -2”, that “50” meant she was 50%, or halfway, effaced.
Effacement is measured in percentages. Like dilation, effacement is a subjective measurement because it is blind, and the way a provider measures it varies.
Because every provider has different finger lengths, we all learn approximately where each effacement measurement hits our finger. It would be very difficult to explain where that is on each person, but in general, a full-thickness cervix is about the length of the tip of the finger to the first knuckle. So for 10% effacement, the cervix would still be almost that full thickness, hitting just above the first knuckle. For 50% effacement, it would be half gone, approximately at the level of the bottom of the fingernail. Once 90% effacement is reached, you can just feel a rim of thickness, and then “complete” effacement is the paper-thin stage.
Picture a balloon. The round part is the main body of the uterus. The part you blow into is the cervix. The “cervix” gets thinner and shorter as more air fills the balloon….so this “cervix” is effacing.
Speaking of balloons…
Here is an excellent demonstration of birth using a balloon and a ping pong ball by Liz Chalmers, a childbirth educator. Notice how the “cervix” of the balloon shortens as the balloon gathers it’s strength at the top just before the “baby” (ball) pops out.
You can see how cervical assessment can be very difficult to accurately assess because, again, it is a blind measure and varies from provider to provider. It is always best to have the same person measure you whenever possible for this very reason. It can be incredibly discouraging to have your effacement “go backwards” after shift change when a new person checks you. (This is one big reason, among many, that I recommend minimizing the number of cervical exams. The last thing a laboring mom needs is discouragement, especially when it might be for no good reason.)
Additionally, not every cervix will start at the same length, and so since we are measuring based on averages, it is possible you have thinned out some when we think you haven’t thinned out at all because your cervix may have started a bit thicker than average.
I hope that helps you understand effacement. Station is the last cervical measurement. Station assesses the baby’s position and we will cover it in the next post.
Do you still have questions? Does it make sense? Let me know below!