Cervical Length Interpreter

In mid-pregnancy, a transvaginal cervical length of 25 mm or less measured before 24 weeks is the standard definition of a short cervix (used by the Society for Maternal-Fetal Medicine and in ACOG's Practice Bulletin 234). It matters because cervical length works like a screen: the shorter the cervix at this stage, the higher the statistical risk of spontaneous preterm birth. It is a risk marker, not a diagnosis and not a prediction — plenty of people with a short cervix go on to deliver at term, particularly once it's found and managed. The value of the number is that it flags who might benefit from a preventive step, so it turns into a conversation with your OB rather than a verdict.

No. A short cervix raises the probability of preterm birth, but it does not mean early delivery is going to happen. Cervical length is one screening measurement taken on one day; risk is a matter of degree, not a yes-or-no. Many people with a short cervix — especially those who start a recommended treatment like vaginal progesterone and are monitored — carry their pregnancies to or near term. That's exactly why it's screened for: finding it early opens the door to steps that lower the risk. The measurement earns you a plan with your provider; it doesn't seal an outcome.

That's a decision for your OB or maternal-fetal-medicine specialist, but the common, evidence-based options are: vaginal progesterone, closer monitoring with repeat cervical-length scans, and — in specific situations — a cervical cerclage, a stitch placed to support the cervix. SMFM recommends vaginal progesterone for a singleton pregnancy with no prior spontaneous preterm birth and a cervical length of 20 mm or less before 24 weeks, and says it's reasonable to consider between 21 and 25 mm through shared decision-making. A cerclage is generally reserved for particular scenarios, most notably a short cervix together with a history of spontaneous preterm birth. Which of these fits you depends on your exact measurement, how many weeks you are, whether you're carrying one baby or more, and your history — none of which a screen can decide on its own.

Yes, significantly. A previous spontaneous preterm birth is itself a major risk factor, and it changes the pathway. For people with that history, guidelines support serial transvaginal cervical-length surveillance across roughly 16 to 24 weeks rather than a single check, so a shortening cervix can be caught as it happens. And when a short cervix is found before 24 weeks in someone who has had a prior spontaneous preterm birth, a cervical cerclage becomes one of the options a provider may discuss, alongside progesterone and monitoring. This is one of the clearest examples of why history is part of the read: the same millimetre number can mean a different plan depending on what came before.

The measurement this tool interprets is a transvaginal ultrasound, which is the accurate, standardized way to measure cervical length — an over-the-belly (transabdominal) view can be misleading, so treatment decisions rest on the transvaginal number. It's often done around the mid-pregnancy anatomy scan (roughly 18 to 22 weeks), and for people at higher risk it may be repeated at intervals through 24 weeks. Screening the cervical length of everyone versus only higher-risk pregnancies varies by practice and provider, so if you're unsure whether you'll be measured, ask at your next visit. Whatever the setting, the number on your own report — taken transvaginally, to standard technique — is the one your OB acts on.

Yes. This tool runs entirely in your browser: the measurement and answers you enter are interpreted on your own device and are never sent to a server, saved, or shared — close the tab and they're gone. We treat pregnancy data as sensitive by design, so there's nothing to delete and no account involved. What you get back is general educational information based on published ACOG and SMFM guidance; it isn't medical advice, a diagnosis, or a substitute for the ultrasound report and the provider who reads it.