What should you know about an antenatal growth scan?

It may be offered when your maternity team wants a closer look at growth, or as part of planned monitoring during pregnancy. The scan is a screening assessment rather than a diagnosis, and its findings are interpreted alongside your pregnancy dates, earlier scans and clinical checks.

The sonographer measures the baby's head, abdomen and thigh bone. These measurements are used to estimate fetal weight and are plotted against the expected range for the stage of pregnancy. A series of scans can show the direction of growth more clearly than a single measurement.

The scan also checks the baby's position, the amount of amniotic fluid and the placenta's location. Doppler ultrasound may be added to assess blood flow in the umbilical cord or other vessels. An estimate can differ from the baby's actual weight, so your clinician considers the whole pattern rather than one figure alone.

Follow the appointment instructions about eating, drinking or arriving with a full bladder, because preparation can vary by stage of pregnancy and clinic. Bring your maternity notes and earlier scan reports if the imaging team does not already have them. Gel is placed on your abdomen and a probe is moved across the skin to create the images.

Afterward, the maternity team may recommend routine follow-up, another growth scan, Doppler monitoring or a review of the pregnancy care plan. A measurement outside the expected range does not by itself explain the cause; repeat assessment can help distinguish a consistent growth pattern from measurement variation.

Contact your maternity unit promptly if your baby's movements are reduced or have changed from their normal pattern. Do not wait for a scheduled growth scan to report this change.

Seek urgent maternity advice for vaginal bleeding, fluid leaking from the vagina, severe or persistent abdominal pain, regular painful tightenings before your expected labour, a severe headache with visual changes, sudden marked swelling, chest pain or difficulty breathing. Use local emergency services if symptoms are severe or you feel acutely unwell.

You could ask how the measurements compare with earlier scans, whether the growth pattern is consistent, whether amniotic fluid and blood flow look as expected, and whether another scan is recommended. If follow-up is advised, ask what will be monitored and which symptoms should prompt an earlier assessment.