Cervical length scans: Why They May Be Offered

A cervical length scan measures the cervix, the lower part of the womb that opens into the vagina. In some pregnancies, this measurement helps the team assess the chance of an early birth and decide whether preventive treatment could help. It cannot predict the exact day your baby will arrive.

Ask why the scan is being offered

A previous spontaneous preterm birth, a later pregnancy loss or certain procedures on the cervix may lead to an early specialist appointment. Tell your midwife about these at booking, even if the details are in another hospital’s records.

The guide to pregnancy after preterm birth explains why the reason for the earlier delivery matters. Monitoring after spontaneous labour can differ from care after a planned early delivery for another complication.

Understand the examination before agreeing

The measurement is usually made with a transvaginal ultrasound probe. Ask the clinician to explain the examination, its purpose and what they need you to do. You can discuss a chaperone, tell them about previous difficult examinations and ask to pause or stop.

Screening in an at risk singleton pregnancy is commonly arranged between 16 and 24 weeks. Twin pregnancies have a different routine screening schedule, with a cervical length scan offered between 16 and 20 weeks. Confirm the dates for your own care rather than copying someone else’s timetable.

Put the result in context

A shorter cervix is associated with a greater risk of preterm birth, but the measurement is only one part of the decision. In the relevant singleton prevention guidance, 25 mm or less is an important threshold. Your history, pregnancy stage and other findings affect what the team recommends.

Possible next steps include further monitoring, prescribed vaginal progesterone or a cervical stitch. These are not interchangeable treatments for everyone with a particular number. The cervical stitch guide offers questions to ask if that procedure is discussed.

Leave with a clear follow up plan

Ask whether another scan is needed, who will explain the result and when any treatment should start. If you are prescribed medicine, obtain written instructions and a contact for problems with the prescription.

A reassuring screening result does not replace assessment of new symptoms. Contact maternity care immediately for possible labour symptoms or leaking fluid before 37 weeks. Do not wait for the next cervical scan to report a change.