Most scans are carried out by specially trained staff called sonographers.
The scan is carried out in a dimly lit room so the sonographer is able to get good images of your baby. You'll then be asked to lower your skirt or trousers to your hips and raise your top to your chest.
The screening test for Down's syndrome used at this stage of pregnancy is called the "combined test".
It involves a blood test and measuring the fluid at the back of the baby's neck (nuchal translucency) with an ultrasound scan.
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Find out more about the combined screening test for Down's syndrome.
It will usually take place at your local hospital ultrasound department.
The person performing the scan is called a sonographer.
You won't be offered the combined screening test if your dating scan happens after 14 weeks.
Instead, you will be offered another blood test between 14 and 20 weeks of pregnancy to screen for the risk of Down's syndrome.