The cervix forms the lower part of the uterus, connecting it to the vagina. It acts as a passageway for fluids and plays a role in reproduction by allowing sperm to enter the uterus. During pregnancy, the cervix remains closed and firm, forming a protective barrier. Its consistency and length are important for maintaining a healthy pregnancy.
Why Cervical Length is Measured
Measuring cervical length assesses the risk of preterm birth, defined as delivery before 37 weeks of gestation. A shorter cervix during pregnancy indicates a higher chance of early delivery.
Healthcare providers may recommend this measurement for individuals with a history of preterm birth or previous cervical procedures, such as a cone biopsy. It is also considered for those experiencing symptoms of preterm labor, including contractions, pressure, or changes in vaginal discharge. Routine screening, typically between 18 and 24 weeks of pregnancy, can help identify individuals at elevated risk, allowing for potential interventions to prolong the pregnancy and improve outcomes.
How Cervical Length is Measured
The most accurate method for measuring cervical length is through transvaginal ultrasound. This procedure involves inserting a thin, lubricated ultrasound probe a few inches into the vagina. The probe emits sound waves that create real-time images of the cervix on a monitor, allowing precise measurement from the internal opening (internal os) to the external opening (external os). To ensure accuracy, the bladder should typically be empty, and minimal pressure should be applied with the probe to avoid artificially lengthening the cervix. Multiple measurements are often taken over a few minutes, with the shortest measurement recorded.
While transvaginal ultrasound is the preferred method for accurate length assessment, a manual examination can also provide information about the cervix. During a manual exam, a healthcare provider uses gloved fingers to assess the cervix’s position, consistency, effacement (thinning), and dilation (opening). This type of examination is less precise for determining the exact cervical length in millimeters. However, it offers valuable clinical insights, particularly regarding how much the cervix has thinned or opened in preparation for labor.
Understanding Your Cervical Length Results
The measured cervical length provides important information about pregnancy progression. A normal cervical length during mid-pregnancy (16-24 weeks) is between 25 and 50 millimeters. At around 20 weeks, the average is approximately 40 millimeters. A cervix measuring less than 25 millimeters before 24 weeks is considered short and associated with an increased risk of preterm birth.
A short cervix indicates that the cervix may be shortening or thinning too early in the pregnancy. This condition can lead to cervical insufficiency, where the cervix begins to dilate prematurely without contractions. If a short cervix is identified, healthcare providers will discuss further monitoring and potential management options. These may include additional ultrasound scans, or medical interventions such as progesterone treatment or a cervical cerclage, which involves placing a stitch around the cervix to help keep it closed.
What to Expect During Cervical Measurement
During a transvaginal cervical length measurement, you will typically lie on an examination table with your knees bent and feet in stirrups, similar to a routine pelvic exam. You may be asked to empty your bladder beforehand, as this can help obtain a clearer image of the cervix. A healthcare provider will cover the thin ultrasound probe with a protective sheath and apply a warm lubricating gel before gently inserting it into the vagina.
The procedure is generally quick, lasting around 15 to 20 minutes. While it is usually not painful, you might experience some pressure or mild discomfort, similar to the sensation of a Pap smear. The technician will carefully move the probe to visualize the cervix from different angles and capture the necessary measurements. After the measurement is complete, your healthcare provider will typically discuss the findings and any recommended next steps with you.