What should you know about an obstetric growth scan?

It can help your maternity team compare measurements with the expected pattern for your pregnancy and decide whether monitoring or planning needs to change.

During the scan, measurements may include the baby's head, abdomen and thigh bone. The clinician may also look at heartbeat, activity, position, the placenta and the amount of amniotic fluid. Doppler assessment of blood flow may be added when clinically appropriate. The estimate is not the same as weighing the baby directly, so your clinician interprets it alongside your dates, examination and earlier scans.

A growth scan can be offered when there is a concern about growth, fluid, placenta or another pregnancy finding. A reassuring scan is useful information, but it does not predict every aspect of labour or newborn health.

Check whether your service wants a full bladder; instructions vary with the pregnancy stage and the type of scan. Bring your maternity notes and a list of medicines or relevant conditions. Wear clothing that allows access to your abdomen. Ask when and how the findings will be discussed. If further scans are suggested, keep those appointments because change over time can be more informative than one measurement.

Do not wait for a scheduled scan if you notice reduced or changed fetal movement, vaginal bleeding, leaking fluid, regular painful contractions, severe abdominal pain, a severe headache, vision changes or sudden swelling. Contact your maternity unit promptly for advice; seek emergency help if you feel seriously unwell or have heavy bleeding.

Ask what prompted the scan, how the measurements compare with earlier checks, whether blood-flow testing was performed, and when the result will guide the next decision. Ask who to contact if movements or other symptoms change.