Short Cervix and Preterm Birth

What is a Short Cervix and How is it Treated?

Pregnant woman going through an ultrasound scan
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What is a Short Cervix?

The cervix, part of a woman's reproductive system, is the lower portion of the uterus. The cervix is long and thick, and should stay long and thick during pregnancy. Sometimes, though, the cervix begins to shorten months before the baby is due to be born. This is called a short cervix.

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.

An insufficient cervix, or incompetent cervix, can cause cervix shortening and therefore premature birth. In insufficient cervix, the cervix is weak and starts to dilate long before the baby is due.

If I Have a Short Cervix, Will My Baby Be Premature?

Women who have a short cervix, with or without funneling, are more likely to have a premature baby than women whose cervixes remain long and thick during their pregnancy. But a short cervix doesn't necessarily mean that your baby will be early! Doctors are much better at treating a short cervix - thereby preventing preterm labor - than they are at stopping premature labor once it starts.

How is a Short Cervix Diagnosed?

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 reliable.

In healthy pregnancies, the cervix is generally between 30 and 50 mm (3 and 5 cm) long. Studies show that the risk of premature birth is greatest when the cervix is less than 25 mm long.

If you have risk factors for premature birth, ask your doctor about having an ultrasound of your cervix.

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

How is Short Cervix Treated?

Because short cervix can increase a mom's risk of premature labor, doctors will usually offer treatment to otherwise healthy women with a short cervix. Treatment for a short cervix may include:

  • Progesterone: Progesterone is a medication that 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 is a stitch placed in the cervix to help it to stay closed. Cerclages may be used in women with short cervix or insufficient cervix.
  • Cervical pessary: A cervical pessary is a silicone 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, may be recommended for women who are at risk for premature birth. However, studies show that activity restriction does not prevent preterm labor in women with a short cervix.

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 short cervix before labor starts, helping to prevent premature birth. It's important to get early and regular prenatal care so that short cervix and other problems with the pregnancy can be found and treated early.

Sources:

Abdel-Aleem, H., Shaaban, O., & Abdel-Aleem, M. (3013). "Cervical Pessary for Preventing Preterm Birth." Cochrane Database of Systematic Reviews, Issue 5.

Crane, J., & Hutchens, D. (2008). "Transvaginal Sonographic Measurement of Cervical Length to Predict Preterm Birth in Asymptomatic Women at Increased Risk: A Systematic Review." Ultrasound Obstet Gynecol 31: 579-587.

Conde-Agudelo, A. et. al. (January 2013). "Vaginal Progesterone Versus Cervical Cerclage for the Prevention of Preterm Birth in Women With A Sonographic Short Cervix, Singleton Gestation, and Previous Preterm Birth: A Systematic Review and Indirect Comparison Meta-Analysis." American Journal of Obstetrics and Gynecology 208(1) 42.e1-42.e18.

Grobman, W. et. al. (June 2013). "Activity Restriction Among Women With A Short Cervix." Obstetrics & Gynecology 121(6) 1181-1186.

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