Guidance

Screening in pregnancy: dating scan

Updated 31 October 2021

Public Health England (PHE) created this information on behalf of the NHS. In this information, the word ‘we’ refers to the NHS service that provides screening.

---

Purpose of the pregnancy dating scan

The pregnancy dating ultrasound scan:

• checks your baby’s heartbeat
• finds out if there is more than one baby
• measures your baby to estimate how many weeks’ pregnant you are
• checks for some conditions in your baby that might be seen at this stage
• is part of the combined screening test for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome, if you choose to be screened

Specially trained staff called sonographers carry out the scan.

Screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome

Screening is your choice. You do not have to have the screening test. Some people want to find out if their baby has Down’s syndrome, Edwards’ syndrome or Patau’s syndrome and some do not. This screening test is called the combined test.

If you choose to have screening for these conditions, the ultrasound scan is one part of the screening test. The second part is a blood test from you. The scan can only be done when your baby is a certain size. The information from these 2 tests is combined to work out the chance of you having a baby with Down’s syndrome, Edwards’ syndrome or Patau’s syndrome.

If you choose to have screening for Down’s syndrome, Edwards’ syndrome or Patau’s syndrome, it is important that you attend appointments for both parts of the test – the scan and the blood test.

If you choose not to have screening for Down’s syndrome, Edwards’ syndrome or Patau’s syndrome, you can still have all the other parts of your usual antenatal care.

Please let a member of staff know if you choose not to have screening or if you want to speak to someone for more information.

Safety of the scan

There are no known risks to you or your baby from having an ultrasound scan. It is important to think carefully if you want to have the scan or not and would want to know the result of the combined test.

The scan

To get clear views of your baby, the scan is performed in a dimly lit room and we might ask you to come with a full bladder.

Having the scan does not hurt, but the sonographer might need to apply slight pressure to get clear views of your baby. This might be uncomfortable. A black and white picture of your baby will then be seen on the ultrasound screen.

The appointment usually takes around 20 minutes.

1. You will be asked to lie on a couch.
2. You will be asked to raise your top to your chest and lower your skirt or trousers to your hips.
3. Tissue paper is tucked into your clothing to protect it from the ultrasound gel. The gel is put on your tummy. The gel may be cold.
4. The sonographer moves a hand-held device called a probe over your tummy to carefully examine your baby’s body. The gel makes sure there is good contact between the probe and your skin.

Sometimes it is difficult to get a clear view of your baby. This might be because your baby is lying in an awkward position or if you are above average weight. This does not mean there is anything to worry about. You will be asked to stand up and move around and one further attempt will be made.

You might be offered a trans-vaginal scan. A transvaginal scan uses a long, thin probe that is covered with a plastic or latex cover and is inserted into the vagina.

The sonographer may be quiet during the scan. It is important for them to be able to concentrate so they can perform a good quality scan.

You may like someone to come with you to the scan. Most hospitals do not allow children to attend scans. Please ask your hospital about this before your appointment.

Possible results of this scan

In most cases, the scan will show that your baby appears to be developing as expected.

You will always be told if anything unexpected is found during your scan.

During your scan, the sonographer might ask for a second opinion from another member of staff.

Occasionally, some conditions can be seen at this early scan, for example, if a baby has anencephaly, a condition where parts of the baby’s skull and brain are missing.

Other conditions are more difficult to see at this stage of pregnancy as the baby is very small. Some conditions only develop later in pregnancy.

If your baby does not appear to be developing as expected, we will refer you to a specialist.

If you choose to have screening, sometimes it is not possible to complete the scan part of the combined test despite the 2 attempts. This might be because:

• your baby is lying in an awkward position
• you are above average weight
• your pregnancy is too advanced

In these cases, your choices of screening are:

1. Screening for Down’s syndrome. This is offered as a blood test between 14 and 20 weeks of pregnancy. This test is called the quadruple test and is not quite as accurate as the combined test.

2. Screening for Edwards’ syndrome and Patau’s syndrome, which is offered as part of the 20-week scan.

3. No screening.

Your personal information

The NHS Screening Programmes use personal information from your NHS records to invite you for screening at the right time. Public Health England also uses your information to ensure you receive high quality care and to improve the screening programmes. Find out more about how your information is used and protected, and your options.