Cervical length: Why does it matter during pregnancy?

Cervical length refers to the length of the lower end of the uterus. During pregnancy, the length of the cervix might shorten too soon, increasing the risk of preterm labor and premature birth. Preterm labor is labor that begins between 20 weeks and 36 weeks and 6 days of pregnancy. The earlier premature birth happens, the greater the health risks for the baby.

Before pregnancy, the cervix — the lower part of the uterus that connects to the vagina — is closed, long and firm. During pregnancy, the cervix gradually softens. As the body gets ready for labor, the cervix decreases in length, and finally opens as the mother prepares to give birth. If the cervix begins to open before 37 weeks, premature birth could occur.

Your health care provider might do an ultrasound to measure your cervical length if you experience signs and symptoms of preterm labor. These include regular or frequent contractions, a constant low, dull backache, a change in the type of vaginal discharge, or pelvic pressure. Your provider might also do a pelvic exam to determine if your cervix has begun to open.

If your ultrasound shows that your cervical length is less than 29 millimeters but greater than 25 millimeters, your health care provider might recommend more frequent ultrasounds to monitor your cervical length. If your cervical length is less than 25 millimeters (short cervix) before 24 weeks of pregnancy and you're only carrying one baby, your health care provider might consider a procedure that uses sutures or synthetic tape to reinforce your cervix (cervical cerclage).

If you have a prior history of premature birth, your health care provider might also discuss the potential benefits of progesterone injections to decrease your risk of another premature birth. Keep in mind that research on the use of progesterone injections is ongoing.

If you're concerned about your cervical length during pregnancy, talk to your health care provider. Your provider can answer your questions and help you understand how to promote a healthy pregnancy.

Last Updated May 28, 2022

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