If you're pregnant in England you'll be offered an ultrasound scan at around 10 to 14 weeks of pregnancy. This is called the dating scan. It's used to see how far along in your pregnancy you are and check your baby's development. The scan may also be part of a screening test for Down's syndrome.

Your midwife or doctor will book you a dating scan appointment. It will usually take place at your local hospital ultrasound department. Most scans are carried out by sonographers.

You may need to have a full bladder for this scan, as this makes the ultrasound image clearer. You can ask your midwife or doctor before the scan if this is the case. The dating scan usually takes about 20 minutes.

What is the purpose of the dating scan?

The purpose of the dating scan is to check:

• how many weeks pregnant you are and work out your due date (the estimated date of delivery, or EDD)
• whether you're expecting more than 1 baby
• that the baby is growing in the right place
• your baby's development

This scan can detect some health conditions, such as spina bifida.

Does screening for Down's syndrome happen at the dating scan?

This depends on whether you have agreed to have the screening and when the scan takes place. Screening for Down's syndrome will happen at the dating scan if:

• you have agreed to have screening for the condition
• the scan takes place between 10 and 14 weeks of pregnancy

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. This is sometimes called a nuchal translucency scan.

The nuchal translucency measurement can be taken during the dating scan. If you have agreed to have screening for Down's syndrome, the dating scan and the screening will usually happen at the same time.

You will not be offered the combined screening test if your dating scan happens after 14 weeks. Instead, you'll be offered another blood test between 14 and 20 weeks of pregnancy to screen for your chance of having a baby with Down's syndrome. This test is not quite as accurate as the combined test.