What should you know about ultrasound dating scan?

A dating scan uses sound waves to create images of the uterus and pregnancy. It may help estimate gestational age, identify whether a heartbeat is visible, check whether the pregnancy is in the uterus and show whether there is one pregnancy or more. The timing estimate is based on measurements and may differ from a date calculated from the last menstrual period, especially when cycles are irregular. An early scan cannot detect every condition and is not the same as a detailed anatomy scan or a nuchal translucency scan.

Bring the date of your last menstrual period if known, details of previous pregnancies and any symptoms or test results. Ask whether the scan will be abdominal or internal; an internal scan may give clearer early images and should be explained beforehand. You may be asked to attend with a partly full bladder for an abdominal scan. Results can be immediate, but uncertain findings may lead to a repeat scan or further review. Write down questions so you can discuss what the measurements mean for your care.

Seek urgent maternity or emergency care for heavy vaginal bleeding, severe or one-sided abdominal pain, shoulder-tip pain, dizziness or fainting. These symptoms need prompt assessment, whether or not a scan has been booked. Contact your pregnancy team for ongoing bleeding, increasing pain or concerns after an internal scan.

Ask: What pregnancy date does the measurement suggest? Was the pregnancy seen in the uterus? Was development appropriate for this stage? Do I need a repeat scan? When should I arrange the nuchal translucency scan?