12 week scan: Your dating scan guide

Although sometimes known as the reassurance and viability scan, your 12 week scan is more typically referred to as the dating scan. Bear in mind that you may not have your scan at exactly 12 weeks; it usually takes place between your 10th and 14th week of pregnancy¹.

During the first scan your sonographer will check the size of your baby to give a more accurate idea how many weeks you’ve been pregnant and your due date. It will provide clarity on whether you are expecting more than one baby and the scan will also determine the ‘viability’ of the pregnancy by confirming that the baby is growing as expected within the womb and developing correctly. The scan is harmless to mother and baby and will typically take 20 to 30 minutes for the sonographer to complete before he or she provides a report for your midwife to share with you.

As part of your first scan at around 12 weeks, you may choose to have the Nuchal Transluceny (NT) scan which is part of the combined screening test for Down's syndrome². The NT scan measures the nuchal fluid at the back of your baby’s neck¹ because babies with Down’s syndrome may have an increased NT. It’s non-invasive and simply a case of the sonographer getting a good enough view of your baby’s neck to take a measurement on screen.

Sadly, for some the scan reveals that their baby isn’t developing as it should, or a heartbeat cannot be found, indicating an early miscarriage. It is an incredibly sad and difficult experience for any woman and her partner to go through, but help and support is available from charities such as miscarriageassociation.org.uk and tommys.org.

At 12 weeks pregnant, your baby is around 5-6cm in length³, with vital organs, bones and muscles in place, ready to grow and mature over the coming months.