Why Cervical Length Matters During Pregnancy
Overview
Cervical length refers to how long the cervix is during pregnancy. The cervix is the lower section of the uterus that connects to the vagina. Its main job is to hold the fetus safely inside the uterus until the baby is ready to be born. Keeping a normal cervical length helps prevent early labor, also called preterm labor, and preterm birth.
Preterm labor starts after 20 weeks but before 37 weeks of pregnancy. If the cervix shortens or opens too soon, the risk of preterm delivery increases. Babies born early face higher chances of health problems, and these risks increase the earlier the birth happens.
What Happens to the Cervix During Pregnancy
Before and early in pregnancy, the cervix stays long, firm, and closed. As pregnancy continues, the cervix slowly softens and shortens in a process called effacement. This change prepares the body for labor. If the cervix shortens too soon—before 37 weeks—premature birth can occur. Often, the cervix shortens early without any symptoms, so regular checks help catch changes in time.
How Cervical Length Is Measured
Doctors use a transvaginal ultrasound to measure cervical length. This scan gives a clear picture of the cervix and lets doctors see if it is starting to shorten. A cervix longer than about 3.5 to 4.0 cm is usually healthy in the second trimester, while anything below 2.5 cm is short and may signal a higher risk for preterm labor.
| Cervical Length | Possible Implications |
|---|---|
| 3.5 – 4.0 cm | Generally normal |
| 2.5 – 3.5 cm | Needs further observation |
| Less than 2.5 cm | Higher risk of early labor |
Why an Early Shortening Cervix Matters
A short cervix can lead to complications. If the cervix becomes too short too soon, it may not be strong enough to keep the fetus inside the uterus until the right time. This situation is called cervical insufficiency. It increases the risk of:
- Preterm labor
- Preterm birth
- Miscarriage in some cases
- Early opening of the cervix without pain
Women who have had these problems before may need closer monitoring. In multiple pregnancies, a short cervix brings even more risk for early delivery.
Symptoms and Monitoring
Often, the cervix shortens without any clear signs. When symptoms of early labor do appear, they might include regular contractions, lower back pain, pelvic pressure, cramps, and changes in vaginal discharge. Doctors may suggest a transvaginal ultrasound if these symptoms or known risk factors are present.
Tools and Treatments
If the cervix measures between 29 mm and 25 mm, doctors may monitor it more often with transvaginal scans. When the cervix is under 25 mm before 24 weeks, extra steps can help lower risk:
- Cervical Cerclage: Doctors place a stitch or band around the cervix to keep it closed, removing it as labor nears.
- Progesterone Therapy: Progesterone hormone supplements can help reduce the risk of preterm birth for some women with a short cervix.
- Pessary: Sometimes, doctors place a small device called a pessary to support the cervix.
Bed rest and activity limits, once suggested, are no longer recommended because research does not show they lower the risk of preterm delivery. The right treatment depends on each person’s risk factors, which doctors review carefully.
Who Is at Greater Risk?
Certain factors increase the risk of a short cervix and early birth:
- Past preterm birth
- History of cervical surgery, such as treatment for abnormal pap tests
- Multiple pregnancies (twins, triplets, etc.)
- Structural or developmental issues with the cervix or uterus
- Short cervix found during a routine ultrasound
Doctors use this information, along with cervical length measurements and medical history, to identify those at higher risk during pregnancy.
The Importance of Routine Care
Regular prenatal visits help monitor cervical health, especially for those with risk factors for preterm labor. Early detection of a shortening cervix lets doctors offer support such as cervical cerclage, hormonal treatment, or extra monitoring as pregnancy continues.
If any symptoms of early labor appear, patients should contact their care team right away. Routine checks and ultrasound scans play a key role, especially in the second and third trimesters, to help protect both mother and baby.
