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Key takeaways

• The 12-week scan is also known as the dating scan.
• It checks your baby's development and estimates your due date.
• It can include screening for certain genetic conditions.
• You may need a full bladder for clearer images.

What is the 12-week scan?

The 12-week scan is an ultrasound scan. It is also called the dating scan. Your midwife or doctor will arrange this appointment for you.

This scan is offered to pregnant people in the UK between 10 and 14 weeks of pregnancy. Its main purpose is to see how far along you are in your pregnancy. It also checks your baby's early development.

The dating scan can also be part of a screening test. This test is for conditions like Down's syndrome. This can include a test that measures the fluid at the back of your baby's neck (a nuchal translucency, or NT, scan).

What to expect during the appointment

Your dating scan appointment will usually take place at your local hospital ultrasound department. Most scans are carried out by sonographers. The scan usually takes about 20 to 30 minutes.

You will lie on your back on a couch during the scan. The sonographer will spread a gel over your tummy.

They will then roll a small scanning device (the probe) over the area. This sends pictures of your baby to a computer screen.

Ultrasound scans use sound waves to create a picture of your baby in the womb. They are safe for both you and your baby.

You may need to have a full bladder for this scan. This can make the ultrasound image clearer. You can ask your midwife or doctor if this is needed for your scan.

What the sonographer checks

The sonographer will check several things during your scan. They will check your baby's heartbeat. They will also confirm if you are expecting more than one baby.

They will check that your baby is growing in the right place. The sonographer will also check your baby's development. This scan can also check for some health conditions, such as spina bifida.

The sonographer will estimate your due date (estimated date of delivery, or EDD). They will work this out based on your baby's measurements. This method is more accurate than using your last period. This might mean that after this scan your pregnancy might be a bit further along, or earlier than you had thought.

Combined screening test

The dating scan may also include a nuchal translucency (NT) scan. This is part of the combined screening test for Down's syndrome. You will also be offered screening for Edwards' syndrome and Patau's syndrome.

The combined test involves a blood test and the NT scan. The sonographer measures a small pocket of fluid at the back of your baby's neck.

This is the nuchal translucency. All babies have some fluid in the back of their neck, but babies with certain conditions often have more.

The blood sample is taken from your arm between 10 and 14 weeks. The NT scan is done between 11 and 14 weeks. If you agree to screening, the dating scan and screening usually happen at the same time.

Understanding your scan results

The measurements from your scan are combined with your blood test results. Your age is also considered. All this information is put into a computer programme. This calculates the chance of your baby having one of the conditions.

Screening tests do not give a definite yes or no answer. They tell you how likely it is that your baby has a certain genetic condition (Down’s syndrome, Edward’s syndrome or Patau’s syndrome). Your results will therefore tell you whether there is a low chance (less likely) or a higher than average chance (more likely) of your baby having one of the genetic conditions.

Most of the results from the combined screening test come back as a lower chance. Around 97% of results fall into this category. If your test results show that you have a lower chance result, you will not need further screening tests.

Higher chance results

Around 3% of screening test results are a higher chance. A higher chance result means it is more likely your baby has a condition. It does not mean your baby definitely has it.

If you have a higher chance result, you have choices.

• You can choose not to have any further tests.
• You can also have another, more accurate, screening blood test (non-invasive prenatal testing, or NIPT).
• Or you can choose to have a diagnostic test.

Non-invasive prenatal testing (NIPT)

NIPT is a blood test that can be done from 10 weeks onwards. It is offered in England, Scotland, or Wales if your combined test result showed that you had a higher chance of your baby having a genetic condition (as described above). NIPT looks at your baby's genetic material in your blood.

This test gives a more reliable prediction than the combined screening. It is not harmful to you or your baby. NIPT does not give a definite yes or no answer.

If the NIPT shows a lower chance, your baby is not likely to have a genetic syndrome as described above (Down's, Edwards', or Patau's syndromes). If the NIPT shows a higher chance, you will be offered a diagnostic test.

Diagnostic tests

Diagnostic tests can tell you for certain whether your baby has a genetic condition. You will be offered a diagnostic test if your combined screening or NIPT gives a higher chance result.

There are two main diagnostic tests:

• Chorionic villus sampling (CVS) – This involves taking a tiny sample of tissue from your placenta.
• Amniocentesis (amnio) – This involves taking a small sample of the fluid from around your baby.

Both of these tests carry a small risk of miscarriage, which is about 1 in 200 (0.5%). You do not have to have a diagnostic test if you do not want one. Your doctor or midwife will discuss your options with you.

CVS is usually offered between 11 and 14 weeks. It can be done later if needed.

Practical tips for your scan

You may need to have a full bladder for your scan. This makes the ultrasound image clearer. You can ask your midwife or doctor before your appointment if this is the case.

You can bring another adult with you to the scan appointment.

Most hospitals do not allow children to attend scans. This is because childcare is not usually available. It's a good idea to check your hospital's policy before your appointment.

Most hospitals will offer you a picture of your baby from your scan. You may need to pay for this. It is a good idea to take some money or a debit card with you.

The sonographer will be able to tell you the results of the scan at the time. If you had the nuchal translucency scan, the results for certain syndromes will be sent by letter. These include Down's, Edwards', and Patau's syndromes.

You can ask your midwife how long it takes to receive these results in your area.