The pregnancy dating scan

All pregnant women are offered an ultrasound scan at around 8-14 weeks of pregnancy. This scan is called the dating scan. It's used to see how far along in your pregnancy you are and check your baby's development.

Your midwife or doctor will book you a dating scan appointment. It will usually take place at your local hospital ultrasound department.

The person performing the scan is called a sonographer.

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 scan usually takes around 20 minutes.

Find out more about what happens during a pregnancy ultrasound scan.

What is the purpose of the dating scan?

The purpose of the dating scan is to:

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

Some abnormalities may also be detected at this scan, such as neural tube defects (spina bifida is a type of neural tube defect).

Does screening for Down's syndrome happen at this 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 11 and 14 weeks of pregnancy

The screening test for Down's syndrome used at this stage of pregnancy is called the combined test. The combined test 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.

Find out more about the combined screening test for Down's syndrome.

You will not 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. This test is not quite as accurate as the combined test.

Find out more about:

• the mid-pregnancy anomaly scan
• screening for Down's syndrome
• ultrasound scans in pregnancy