Cervical Scan

The cervix is the lower part of the womb (uterus) that stays closed and firm through most of pregnancy, then gradually softens and shortens as your body prepares for labour. A cervical length scan simply measures how long the closed part of the cervix is, in millimetres, using a transvaginal scan.

Evidence has consistently shown that a cervix that shortens in the middle of pregnancy is one of the clearest early signs that a baby may arrive too soon. In England and Wales around 8 in 100 babies — roughly 1 in 13 — are born preterm, meaning before 37 completed weeks: 7.9 per cent of live births in 2022, according to the pregnancy charity Tommy's. Prematurity remains a leading cause of health problems in newborn babies.

The relationship is a gradual, continuous one: broadly, the shorter the cervix, the higher the chance of preterm birth. NICE guidance considers a cervix measuring 25 mm or less before 24 weeks to be short, and the associated risk rises further as the measurement falls.

Measuring cervical length does not, in itself, cause or prevent early labour. Its value lies in identifying the pregnancies that may benefit from closer monitoring or preventive treatment, giving your maternity team time to act. Any measurement is interpreted by specialist fetal medicine clinicians in the context of your wider history, never by the number alone.

Cervical Scan is important for women who have an increased risk of delivering their baby preterm such as:

• Spontaneous preterm birth before 34 weeks or late miscarriage
• Surgery on their cervix or womb (other than cesarean section)
• Having previous delivery by urgent cesarean section which was performed during full dilatation
• Abnormal shape of the womb like heart-shaped (bicornuate uterus) or other uterine anomalies
• Other indications

Cervical length is most informative during the second trimester. It is usually assessed from around 16 weeks up to about 24 weeks of pregnancy — the window in which a shortening cervix gives the most useful warning of preterm birth risk.

For many women the measurement is taken at the same appointment as the 20-week anomaly scan, when your baby's anatomy is examined in detail. At London Pregnancy Clinic it can equally be added to an early fetal scan, a growth scan or any other fetal scan you are having — on request, we include a cervical assessment with any scan between 14 and 34 weeks, at no extra charge.

If you have risk factors for early birth, your maternity team may recommend a series of measurements rather than a single one — for example every two to four weeks, and sometimes more often, until around 24 weeks — so that any change is spotted early. Because we measure the cervix within a full fetal scan, your baby's wellbeing is checked at each visit too.

Whether cervical surveillance is right for you is a decision to make with your midwife, GP or obstetric team, who can advise based on your individual history.

The only correct way to measure the cervix is by transvaginal scan (TVS). This approach represent a unique window to check the structures deeply hidden in your pelvis and poorly visible by transabdominal scan. Those structures are lower part of the womb, presenting (lower) parts of the baby and other intrapelvic structures.

We are not narrow minded and at Cervical Scan will offer you also checks for vasa previa, placental position and abnormalities and if you had previous cesarean section(s) will check the relationship between the scar(s) and the placenta. We will also check the parts of your baby which may be better visible by transvaginal approach.

The additional scan of important structures is fast and usually add little to the overall time of transvaginal examination of the cervix. You can also decide not to check additional structures and to have only the measurements of the cervical length.

A cervical length above 25 mm in the second trimester is reassuring and falls within the normal range for most pregnancies. Usually no further action is needed, although your team may still suggest a repeat scan if you have particular risk factors.

A cervix measuring 25 mm or less before 24 weeks is generally described as short. A short or funnelling cervix is sometimes referred to as cervical incompetence or cervical insufficiency — a weakened cervix that may begin to open too early. A short measurement does not mean your baby will be born early — many women with a short cervix go on to have a full-term birth — but it does mean that extra care may be recommended to reduce the risk.

Sometimes a scan shows funnelling, where the internal opening of the cervix begins to widen into a Y, V or U shape while the lower part stays closed. Funnelling is weighed alongside the overall cervical length by specialist fetal medicine clinicians when your risk is assessed; on its own it is not a diagnosis.

Where a short cervix is found, recognised options that your NHS or private obstetric team may discuss include vaginal progesterone, a cervical stitch (cervical cerclage), and closer monitoring through a preterm birth prevention clinic — approaches set out in NICE and RCOG guidance. The most suitable approach depends on your history and is always a shared decision with your doctor.

London Pregnancy Clinic provides a detailed report for your obstetric team so that any follow-up can be arranged promptly. As a diagnostic scanning service, we do not prescribe treatment ourselves. If you have concerns about your pregnancy or your baby's wellbeing, contact your midwife, GP or maternity unit promptly. You may also find our obstetric care and private maternity care pages helpful.

This information is intended for general educational purposes only and does not constitute medical advice. Please consult a qualified healthcare professional for guidance specific to your individual circumstances.

If you have an indication for cervical length measurements we can perform cervical assessment and cervical length measurements during any of our fetal scans.

Our philosophy is to perform the best imaging possible in any specific situation. We do not add any surcharge for the transvaginal scans, even taking into consideration that those types of scan are time consuming and require special expertise.

This means that if you require a measurement of the cervical length during the anomaly scan (or any other scan) you still will pay only the basic price of the anomaly scan.

Please note we are not performing a scan of your cervix without checking the anatomy and wellbeing of your baby so you cannot have a scan just measuring the cervical length.