The cervix is the neck of the womb (uterus). During a healthy pregnancy, it stays long and closed, helping to support the pregnancy until the baby is ready to be born. As labour approaches at term, the cervix naturally softens, shortens and then opens to allow delivery.

In some pregnancies, the cervix may become short earlier than expected, sometimes from the second trimester. This is linked with a higher chance of late miscarriage or preterm birth. In general, the shorter the cervix, the higher the risk of early delivery.

Assessing the cervix during pregnancy is important because if early shortening is identified, treatments such as progesterone pessaries or a cervical stitch can be offered. These treatments can help reduce the risk of preterm birth.

A cervical length scan is an ultrasound examination that measures the length of the cervix. The most accurate way to do this is with a transvaginal ultrasound scan, where a small ultrasound probe is gently placed into the vagina to obtain a clear and reliable measurement.

The cervix is best assessed using a transvaginal ultrasound scan. This approach allows the cervix to be seen clearly and measured accurately.

An abdominal scan does not always give a clear view of the cervix and can lead to inaccurate measurements. For this reason, transvaginal scanning is recommended when assessing cervical length.

Yes. Transvaginal ultrasound is safe in pregnancy and does not increase the risk of miscarriage, infection or preterm labour.

Cervical length assessment is usually performed between 16 and 24 weeks of pregnancy, which is the best time to identify early cervical shortening.

In women with risk factors, monitoring may start earlier, from around 14–16 weeks, and may be repeated every two weeks until 24 weeks. In women without known risk factors, the scan is often performed around 20–22 weeks, usually alongside the anomaly scan.

Cervical length assessment is an important part of holistic pregnancy care and can be offered to all women.

It is particularly important for women with risk factors such as:

• Previous late miscarriage or preterm birth
• Previous treatment to the cervix (for example LLETZ for abnormal smear tests)
• A history of a short cervix in a previous pregnancy
• An unusually shaped womb (such as a bicornuate womb)
• Caesarean delivery at full dilation in a previous pregnancy

However, cervical shortening can also occur in women with no obvious risk factors.

Between 16 and 24 weeks of pregnancy, a cervical length of more than 25 mm is considered reassuring. In pregnancies that reach full term, the average cervical length is usually around 30–32 mm. In general, a longer cervix is more reassuring.

If a short cervix is identified, your options will be discussed in detail with a Fetal Medicine consultant. Management may include closer monitoring, treatment with progesterone, or consideration of a cervical stitch, depending on your individual situation.

No. A short cervix means the risk of preterm birth is higher, but many women with this finding go on to have healthy pregnancies and deliver at or near term with appropriate monitoring and treatment.

Yes. Most cervical length scans are reassuring. Your results will be explained clearly during your appointment, and you will have time to ask questions and discuss what the findings mean for you and your pregnancy. If any follow-up or treatment is needed, this will be discussed carefully, with a personalised plan to support you and your baby throughout the remainder of your pregnancy.