Effacement is the thinning of the cervix, and is expressed generally as a percentage. 80% percent effaced, for example, indicates that the cervix has thinned out 80% and still has another 20% to thin out completely. Effacement can precede or accompany dilation.
Dilation or dilatation (depending on your preference of terminology) is the opening of the cervix. Generally 1 fingertip-breadth (of the provider who is checking you) equates to 1 cm of dilation, 2 fingertips equals 2 cm, and so on, all the way up to 10 centimeters (or "complete"). The provider actually sticks their fingertips into the cervical opening to check this measurement.
Many times the vaginal exam is used to guess how much longer a woman may have left before the baby will be born. Unfortunately, this is a poor indication because every woman dilates and progresses at her own pace. There are many factors that affect labor progress, and it's unrealistic to rely on cervical checks to predict the future. I believe vaginal exams are a small part of our modern world's effort to control labor, combined with the use of medications to start and speed up labor to try and fit it into our schedules and what we think labor should look like.
Vaginal exams are uncomfortable in the least, and sometimes downright painful. At times during labor the provider may want to do a vaginal exam at the height of a contraction, which makes it even more uncomfortable. From my experience, it can also interfere with the laboring woman's focus and coping techniques and make it harder for her to work through the contraction.
Vaginal exams can be harmful. Yes, you read that right. Downright dangerous. When anything is inserted into the vagina (gloved or not) it brings bacteria from the outside of the body into the birth canal. Our bodies have different types of bacteria in different places, and they're not meant to be mixed up and put in places where they aren't normally found. This can cause maternal infection and fever, particularly if the bag of waters has already ruptured.
If your has water broken (before or during labor) and you want to avoid the risk of infection, AVOID VAGINAL EXAMS.
The reason hospitals have time limits on labor (baby must be born within 12, 24, or X number of hours after rupture of membranes) is because of this risk of infection. If you avoid vaginal exams (or anything that could contaminate the birth canal) you may virtually eliminate this risk, and you can safely wait for labor to start and progress on its own.
I've covered the risk. Now let's talk about the alternatives.
How Dilated Am I? Assessing Dilation in Labor WITHOUT an Internal Exam.: This is a really good blog post outlining multiple ways of checking labor progress without an intrusive vaginal exam. These methods include closely observing outward signs from the mother including the sound of her voice, smells, irrational thinking, feeling the top of the uterus, and more. I've found it to be extremely helpful.
Checking dilation without a vaginal exam: I love this post, as it outlines very specifically how to use touch to measure the space between the top of the fundus (uterus) to the breastbone:
"During a contraction and with mom on her back, determine how many fingerbreadths of space are between the fundus [top of the uterus] and xiphoid process [the triangular tip of the breastbone] at the height of a contraction.
5 fb = no dilation
4 fb = 2 cm
3 fb = 4 cm
2 fb = 6 cm
1 fb = 8 cm
0 fb = complete"
My understanding is that it's best to use the fingerbreadths of the mother herself, but someone else can check the measurement as well.
Isn't that great?! These posts give great information that can help empower women to stay comfortable and safe in labor, and also arm them with tools to help them in the process.
Here is another article outlining The Dangers of Vaginal Exams if you want to learn more.