What is a short cervix?

Pregnancy is a time when most women learn all sorts of new things about their bodies. During routine gynecological exams, a gynecologist should test for abnormalities within the cervix, a round piece of tissue connecting the vagina and the uterus. This small opening is very important for childbirth, as it dilates to allow a baby to pass through.

Studies have found that the length of a woman’s cervix at 20 to 24 weeks is actually one of the best predictors of preterm birth. During normal pregnancy, a woman’s cervix measures between 3 and 5 cm. When a woman has a cervix shorter than 2.5 cm, she is at risk for preterm delivery. This is because a short cervix may thin and dilate too soon, encouraging a baby to be born too early. 

When to check?

The best time to test for a short cervix is between weeks 16 and 24. While most ultrasound technicians will measure the cervix in this period, you should ask your ultrasound technician to measure your cervix just in case. The cervix may be measured using an ultrasound probe on your abdomen, or inside the vagina.

Most women with short cervixes go on to deliver perfectly healthy babies full-term. If you do have a short cervix, there are several options your provider may recommend to you to ensure a baby is carried to term. Vaginal progesterone is a prescription medication that has been shown to significantly reduce the risk of preterm delivery. Your provider may also prescribe bed rest, although this is generally no longer recommended because it doesn’t help, and in extreme cases a procedure called cerclage, during which the cervix is sewn together to strengthen it.

Babies born prematurely are at higher risk for several developmental disorders, which is why it’s important to carry a baby longer than 37 weeks to ensure they get all the nutrients and development inside mom as they need.

Reviewed by the Ovia Health Clinical Team


  • Shannon K Laughlin-Tommaso. “Cervical length during pregnancy: Why does it matter?” MayoClinic. Mayo Foundation for Medical Education and Research, May 2015. Web.
  • “Cervical insufficiency and short cervix.” MarchofDimes. March of Dimes Foundation, Aug 15. Web.
  • James P Nott, et al. “The structure and function of the cervix during pregnancy.” Translational Research in Anatomy. Vol 2:1-7. Web. Mar 2016.
  • “Preterm (Premature) Labor and Birth” ACOG. FAQ087 from American College of Obstetricians and Gynecologists, Nov 2016. Web.
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