Short Cervix and Preterm Birth Overview

Pregnant woman getting an ultrasound

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In This Article

The cervix is the lower portion of the uterus that functions as a "door" between the womb and the vagina. Primarily composed of fibromuscular tissue, the cervix is normally long, firm, and thick and should stay that way for the majority of pregnancy. Sometimes, though, the cervix begins to shorten months before the baby is due to be born. This is called a short cervix.

Overview

Pre-pregnancy, the cervix is typically four to five inches in length. During pregnancy, the cervix keeps the baby secure in the uterus until it begins to soften and shorten to prepare for labor. When the cervix shortens prematurely, this increases the risk of delivering too soon.

The cervix has two main openings. The internal opening, or internal os, is at the top of the cervix, closest to the uterus. The external opening, or external os, is at the bottom of the cervix. Sometimes, when the cervix begins to shorten, the internal os begins to dilate and the cervix changes from a "v" to a "u" shape. This is called cervical funneling.

Causes

The main causes of a short cervix and cervical funneling include heredity, trauma, abnormalities of the cervix or uterus, or having an insufficient cervix (also called incompetent cervix). An insufficient cervix is when your cervix opens or dilates too early and is a common cause of premature birth. This condition can cause the cervix to shorten as well, in essence preparing the cervix for labor before it should.

With an insufficient cervix, the cervical tissue is weak and starts to dilate long before the baby is due.

Will My Baby Be Premature?

Women who have a short cervix, with or without funneling or insufficiency, are more likely to have a premature baby than women whose cervixes remain long, firm, and thick for the duration of their pregnancies. However, a short cervix doesn't necessarily predetermine that your baby will be early.

There are multiple interventions available for a short cervix that doctors can use to reduce your risk of preterm labor. It's key to know that it's easier to treat a short cervix—and prevent preterm labor—than stop premature labor once it has begun. The key is diagnosing the condition before it leads to early labor.

Diagnosis

The best way to diagnose a short cervix is with an ultrasound. Doctors can't diagnose a short cervix or funneling with a manual exam. Only an ultrasound is a reliable way to make this determination. However, in routine pregnancies, doctors don't always check for a short cervix.

If you have risk factors for premature birth and/or a history of miscarriage, ask your doctor about having an ultrasound of your cervix to rule out a short or incompetent cervix. In healthy pregnancies, the cervix is generally between 30 and 50 millimeters (3 and 5 centimeters) long and will stay firm until the end of pregnancy.

Studies show that the risk of premature birth is greatest when the cervix is less than 25 millimeters long.

When detected early, there are effective treatments that can help prevent preterm birth in women with a short cervix or cervical insufficiency.

Treatment

Because a short cervix can increase a pregnant person's risk of premature labor, doctors will usually offer treatment to otherwise healthy people with this condition. Here is an overview of some of the most common treatment options.

Progesterone

Taking progesterone, a key hormone for maintaining pregnancy, has been proven to reduce the risk of premature birth in women who have a short cervix. Progesterone can be given as a weekly shot or as a daily vaginal medication.

Cervical Cerclage

A cerclage or cervical stitch is a suture placed in the cervix to help it stay closed, which studies show can reduce the risk of premature labor. Cerclages are often used in women with a short cervix or insufficient cervix. The procedure is typically done transvaginally, although it is occasionally done through an incision in the abdomen as well.

Cervical Pessary

A cervical pessary is a synthetic band that holds the cervix closed. The cervical pessary is a newer intervention, but studies show that it works well to prevent preterm labor in women with a short cervix. Unlike cerclage, placement of a pessary is not a surgical procedure.

Bed Rest 

Activity restriction, including bed rest, is often recommended for women who are at risk for premature birth. However, bed rest has not proved to help stave off labor for women with a short cervix, so it is usually unnecessary for those with this condition.

Studies show that activity restriction does not prevent preterm labor in women with a short cervix.

A Word From Verywell

If you are diagnosed with a short cervix, you're not alone. The good news is that doctors are getting much better at diagnosing and treating a short cervix before labor starts, helping to prevent premature birth. It's important to get early and regular prenatal care so that a short cervix and any other pregnancy issues can be found and treated early.

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  1. Conde-agudelo A, Romero R, Nicolaides K, et al. Vaginal progesterone vs. cervical cerclage for the prevention of preterm birth in women with a sonographic short cervix, previous preterm birth, and singleton gestation: A systematic review and indirect comparison metaanalysis. Am J Obstet Gynecol. 2013;208(1):42.e1-42.e18. doi:10.1016/j.ajog.2012.10.877 

  2. Pratcorona L, Goya M, Merced C, et al. Cervical pessary to reduce preterm birth <34 weeks of gestation after an episode of preterm labor and a short cervix: A randomized controlled trial. Am J Obstet Gynecol. 2018;219(1):99.e1-99.e16. doi:10.1016/j.ajog.2018.04.031

  3. Grobman WA, Gilbert SA, Iams JD, et al. Activity restriction among women with a short cervix. Obstet Gynecol. 2013;121(6):1181-6. doi:10.1097/AOG.0b013e3182917529

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