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 Pap smears]," 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 (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."