Dating Scan

If you’re unsure about your dates and are unable to establish when you fell pregnant, you may be offered an ultrasound scan to estimate your conception date according to your baby’s size.

Scans carried out during the first trimester (weeks 0-12) are fairly accurate at establishing this information because babies tend to grow at the same rate during the first trimester.

It may be important for you to have a reasonably accurate date if you are at risk of having a baby with an abnormality and are planning to have tests for Down syndrome and/or spina bifida, since the accuracy of these tests depend on when they’re performed.

What happens at an ultrasound scan?

At an early scan you may be asked to drink plenty of water beforehand, to raise your uterus up out of your pelvis and enable the sonographer to see as much as possible. You’ll lie on your back and some clear gel will be smeared on your stomach – this helps the ultrasound transducer’s contact with your skin.

Sometimes in early pregnancy an abdominal ultrasound cannot pick up much because your baby is still too small. If this is the case you may have a transvaginal scan. A probe transducer is inserted into your vagina to see a clearer picture of how your baby is growing. The probe doesn’t hurt, but will likely feel cold.

You should be informed of what the sonographer is doing and you should feel able to ask questions about what you can see. You’ll be presented with your baby’s first picture at the end of the scan!

To see what happens at later scans see antenatal scans for more information. Visit our Early Pregnancy area for all your pregnancy queries answered.

The information in this feature is intended for educational purposes only. If you have any concerns about your health, the health of your child or the health of someone you know, please consult with a doctor or other healthcare professional.