Obstetric dating scan: what to know

The sonographer may assess the pregnancy location, whether a heartbeat is visible, the number of pregnancies and measurements used to estimate gestational age. The scan may also help explain bleeding or pain, but it cannot answer every question about pregnancy health. Dates based on the scan can differ from a calculation using the last menstrual period, especially when cycles are irregular or the date is uncertain. The clinician will explain what was visible at the appointment and whether a repeat scan is needed.

Ask the booking team whether your bladder should be full, as preparation depends on the equipment and stage of pregnancy. Wear clothing that allows access to the lower abdomen. You may be asked questions about your cycle, symptoms and previous pregnancies. Measurements are taken through the abdomen in many appointments; an internal scan may be discussed when an early view is clearer that way. You can ask for an explanation of each step and bring someone if the service allows it.

Do not wait for a routine scan if you have heavy bleeding, severe or one-sided abdominal pain, shoulder-tip pain, fainting, dizziness or feel acutely unwell. Contact your maternity service promptly for concerning symptoms even if a scan is booked. An early scan may provide useful information, but symptoms still need clinical assessment.

Ask what the measurements indicate, whether the estimated due date changes, what could not yet be seen, and when follow-up is recommended. Clarify which symptoms should prompt urgent assessment before the next appointment.