The Basics of Dilation
A nurse or provider measures cervical progress serially throughout labor in most labor settings. The measurement has three parts. First of all is dilation. Dilation is a measure of how “open” the cervical portion of the uterus has become. Dilation takes place over a period of time as the body begins and progresses through labor.
The uterus is the organ that carries a baby as it is developing from implantation until birth. It is made up of involuntary muscle tissue that “squeezes” (contracts) the baby out over time during labor. The cervix is the bottom portion of the uterus. This neck-like section stays closed tight under normal conditions until the baby is fully developed and ready to be born.
Many people think of the cervix like it is a purse-string opening that widens, but really the uterus completely changes shape during labor, pulling the mass of the organ up to the top (fundus) as labor progresses. This makes the top of the uterus very strong to push the baby out with contractions. This pulling back of the uterus is actually what leads to the dilation of the cervix.
You probably know that the measurement of dilation is subjective because it is not something you can see, so there is some variation from one person to another. Nurses and providers assess dilation blindly with their fingers during a vaginal exam. A vaginal exam involves the examiner inserting two fingers into the vagina and then reaching up to the bottom of the uterus (the cervix) and measuring the approximate amount of opening that has happened with the tips of the fingers. This assessment can be quite uncomfortable for the mother in the early stages of labor because the cervix tends to point towards the spine for quite some time.
As mentioned, we measure three things to assess labor progress:
dilation (# of cm) / effacement (%) / station (+/-)
Dilation is the first number. Therefore, if you’ve ever heard a provider say something like, “She’s 3, 50, -2”, that “3” meant she was 3cm dilated.
We measure cervical dilation in centimeters, so you can look at a ruler for reference. Again, remember these measurements are very subjective. I’ll give some visual descriptions for some of the measurements for reference. They are based on my finger size, which is probably a little bigger than the average female hand.
1 cm = just the tip of one finger can fit into the opening of the cervix
(the width of a Cheerio)
2 cm = the tips of two fingers can fit into the opening tightly
(the top of a Young Living Oil bottle)
3 cm = two fingers can fit into the opening with a little wiggle room
4 cm = two fingers easily fit into the opening and can begin to slide apart
5 cm = two fingers easily fit with approximately 3 cm between them
(the bottom of a standard cup of applesauce)
6 cm = two fingers easily fit with approximately 4 cm between them
(the top of a cup of Papa John’s Garlic Sauce – can you tell what we had for dinner last night??)
7 cm = two fingers easily fit with approximately 5 cm between them
8 cm = there is approximately 1 cm of cervix felt all the way around – most of the cervix is gone
(the top of a standard 11oz. coffee mug)
9 cm = The cervix is almost completely gone with just a rim remaining all the way around
10 cm = “Complete” = The cervix is completely gone
The mother who is laboring naturally will experience the urge to push sometime near complete dilation. The baby will begin making its final descent and the mother will reflexively push to help the baby down.