First Pregnancy | All About the Cervix

Pregnancy brings this tiny organ to the forefront of our minds, as the cervix softens, lengthens, elongates, dilates, thins and does all sorts of interesting things. So just what is the cervix and exactly what is its role in pregnancy? The following questions and answers will tell you what you need to know about this very important piece of our anatomy.

What is the cervix anyway?

The cervix is the opening to the womb. It’s located between the vagina and the uterus and plays a crucial role in pregnancy and labor. During pregnancy, it remains closed and the opening is blocked with a mucus plug.

How big is the opening of the cervix?

According to Dr. Adelaide Nardone, medical advisor to the Vagisil Women’s Health Center and clinical instructor at the Brown University School of Medicine, it depends on whether the woman has had a vaginal delivery or not.

“If a woman has never had a baby, her cervical opening is very small, in some cases as small as a pinhead, but large enough to allow for menstrual blood to flow out and to allow for the insertion of a cytobrush [used when obtaining Papsmears],” says Dr. Nardone. “If a woman has had a vaginal delivery, the external opening of the cervix can be described as a small ‘slit’ or ‘fish mouth,’ but the internal ‘os’ [the junction between the cervix and the uterus] should be closed.”

How does the cervix transform during pregnancy?

According to Dr. Nardone, the cervix is the structure that is intended to protect the fetus during its development. It is designed to remain firmly closed and provide resistance to pressure from the growing structures above it (e.g., the fetus and uterus).

“Once labor ensues, the cervix must be able to yield to the intrauterine pressure and contractions and undergo dilatation and effacement [thinning out],” says Dr. Nardone. “The main component of the cervix is collagen, and this provides its firm consistency during gestation.”

The influx of hormones that a progressing pregnancy creates causes the external os (opening of the cervix) to shorten and even open slightly. The internal os becomes more prominent, but thinner walled

What does it mean when your cervix has “ripened”?

“As the pregnancy approaches term, the cervix begins to ‘ripen,'” says Dr. Nardone. “This occurs when the cervix gets a higher water content along with more vascularity. This makes the cervix softer and even cyanotic (blue in color). These changes allow the cervix to stretch and thin to the point that it is capable of responding to the mechanics of labor contractions. During labor, the cervix usually goes from being closed to 10 centimeters dilated so that the baby’s head can progress out of the uterus and into the vagina.”

What does it mean when the cervix is short?

“Usually the pregnant uterine cervix is greater than or equal to 3 centimeters in length,” says Dr. Nardone. “This can be determined clinically by an exam from an OB provider, or it can be determined more accurately by a transvaginal ultrasound. With an ultrasound, the cervix can actually be visualized and measured. If the cervical length measures less than 3 centimeters, this may be an indication of a potential problem such as an incompetent cervix and may signal the possibility of premature delivery. This finding warrants close follow-up.”

What is an incompetent cervix?

The cervix is designed to shorten and widen with your pre-labor contractions. If it does this without contractions it is said to be incompetent. If the cervix is unable to remain closed during pregnancy, this may cause preterm labor.

What is a cervical cerclage?

If a doctor decides your cervix is incompetent, he may suggest a cervical cerclage. This means stitches will be placed in your cervix to hold it closed. It is extremely rare; only about 1 percent of women have to have this procedure.

Is the cervix what dilates and gets measured? What happens if it doesn’t?

“When a woman is checked in labor, it is the cervix that is evaluated as well as the station presenting part [usually the head],” says Dr. Nardone. “The cervix is evaluated for its thickness and dilatation. An example is that a cervical exam reveals the cervix to be 5 centimeters dilated and 75 percent effaced, with the head in 0 station. Normal labor progress occurs when there are regular contractions along with progressive cervical changes. If these don’t occur, the OB provider has to evaluate the woman’s labor and progress and determine what the problem is, such as poor quality contractions, a baby that is too big, a very tense patient, etc.”

Can women have a cervix opening that is too small?

According to Dr. Nardone, the size of the cervical opening prior to or during pregnancy does not determine if a woman progresses in labor or not. “It is the quality of the contractions, the size of the baby and the baby’s presentation and station that allow the cervix to dilate,” she says. “There are rare cases whereby a woman has a stenotic cervix, which means it is tightly shut and does not dilate at all. This can be due to scarring that could be the result of some type of infection, surgery, radiation treatment or genetic anatomic abnormality. Again, this is a rare finding.”

What is the mucous plug?

According to Dr. Oleg Bess, an OB/GYN from Olympia Medical Center in Los Angeles, Calif., the mucous plug is a collection of mucus just inside the cervix. “When the cervix begins to dilate, some of this mucus may come out,” says Dr. Bess. “The mucous plug is an early indicator of labor.”

Does the cervix come forward or down during pregnancy?

“The entire uterus prolapses after a vaginal delivery,” says Dr. Bess. “Sometimes it is so low that the cervix can be felt near the outside of the vagina.”

As you can see, the cervix plays a crucial role in a normal delivery. The more you know about this organ during pregnancy, the better you are able to understand what your doctor is talking about.

Cervix Definitions

Cervix: The organ located between the vagina and the womb.

Os: The opening of the cervix into the body of the uterus. There is the external os, which is the opening on the vaginal side of the cervix, and the internal os, which is the opening on the uterus side of the cervix.

Mucous plug: A collection of mucus that seals the os. It is there to protect the baby from germs.

Incompetent cervix: A cervix that does not remain closed during the course of the pregnancy. The cervix is only supposed to open with the onset of labor.

Cervical cerclage: The procedure that increases tissue resistance in an incompetent uterine cervix usually in the form of stitches in the cervix.

Effacement: The thinning and softening of the cervix that allows the cervix to open.

Dilate: The stretching and widening of the cervix.