Screening in Pregnancy

Pregnancy comes with a lot of choices. And some of the first choices you're offered are about screening. You might be offered blood tests, ultrasound scans or other screening tests without really being sure what they're looking for, whether you have to have them, or what happens if a result comes back showing a higher chance of something. So let's take a step back. What is screening? What tests are offered during pregnancy? And what does a screening result actually mean?

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What is Screening?

 

Screening tests are designed to identify people who have a higher chance of having a particular health condition. They don't usually tell you for certain whether you or your baby has a condition. Think of screening as a way of identifying who might benefit from having more information or further testing. This means that: A higher-chance screening result does not mean your baby definitely has the condition.

And: A lower-chance screening result does not guarantee that your baby does not have the condition.

 

Screening tests aren't perfect. They can sometimes produce false-positive results, where a test suggests a higher chance even though the condition isn't present, or false-negative results, where a lower chance is given even though the condition is present. This distinction becomes particularly important when you're thinking about what you might do with a screening result.

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Screening vs Diagnostic Testing

 

These two terms are easy to mix up.

 

Screening

Screening asks: "How likely is it that this condition might be present?" The result is usually expressed as a chance or probability.

 

Diagnostic testing

Diagnostic testing asks: "Does this condition actually appear to be present?" Diagnostic tests can provide a much more definite answer.

For example, if antenatal screening suggests your baby has a higher chance of having a chromosomal condition, you may be offered a diagnostic test such as chorionic villus sampling (CVS) or amniocentesis.

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These are different from screening tests and involve their own benefits, limitations and risks. You don't need to make any decisions about diagnostic testing before you've even had screening. One step at a time.

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What Screening is offered during Pregnancy?

 

In England, the NHS offers a number of screening tests during pregnancy. These include screening for:

• Hepatitis B, HIV and syphilis

• Sickle cell and thalassaemia

• Down's syndrome, Edwards' syndrome and Patau's syndrome

• Certain physical conditions in your baby through the 20-week screening scan

• Diabetic eye disease if you have type 1 or type 2 diabetes

 

Let's look at these in a little more detail.

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Screening for Infectious Diseases

 

Early in pregnancy, you'll usually be offered blood tests for:

• Hepatitis B

• HIV

• Syphilis

 

These tests are usually offered at your booking appointment, generally between 8 and 12 weeks. The purpose is to identify infections where knowing about them during pregnancy can allow you and your maternity team to offer appropriate care and reduce the chance of passing the infection to your baby. These tests are different from some of the screening tests you may hear discussed in relation to chromosomal conditions. They're still screening, but the purpose and what happens following a result are different. If you're offered these tests, your midwife should explain what they're testing for and what the results could mean.

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Screening for Sickle Cell and Thalassaemia

 

You may also be offered screening for sickle cell disease and thalassaemia. These are inherited blood conditions. Screening usually begins with a blood test. Depending on your result and circumstances, the baby's biological father may also be offered testing and you may be offered further information or testing.

 

The aim is to identify whether you or your baby may have a higher chance of having one of these conditions so that you can be offered appropriate information and further testing if needed. If you have a family history of sickle cell disease or thalassaemia, or know that the baby's biological father is a carrier, make sure your midwife knows.

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Screening for Down's Syndrome, Edwards' Syndrome and Patau's Syndrome

 

This is one of the areas where the word "screening" is particularly important. The NHS offers screening for:

• Down's syndrome

• Edwards' syndrome

• Patau's syndrome

 

The first-stage test is usually offered between around 10 and 14 weeks. It is called the combined test and involves:

• A blood test

• An ultrasound measurement taken during the 11 to 14-week scan

 

The ultrasound looks at the amount of fluid at the back of your baby's neck, known as the nuchal translucency measurement. The blood test and ultrasound information are combined with other factors to calculate the chance of your baby having one of these conditions. If it isn't possible to have the combined test, a quadruple test may be offered between 14 and 20 weeks. This is a blood test that screens for Down's syndrome and is less accurate than the combined test. 

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What does a Screening Result actually Mean?

 

This is where things can get confusing. You may be given a result that looks something like: 1 in 500 or: 1 in 50

 

These are estimates of the chance that your baby has the condition being screened for. They are not a diagnosis. For example, a result of 1 in 500 means that, statistically, around 1 baby in 500 with that screening result would be expected to have the condition. A result of 1 in 50 means the estimated chance is higher. But even a "higher chance" result does not mean that your baby definitely has the condition. And a "lower chance" result does not mean the condition has been ruled out completely. This is why the language around screening matters. Higher chance does not mean "your baby has it". Lower chance does not mean "your baby definitely doesn't".

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What happens if a Screening Result shows a Higher Chance?

 

If your screening result suggests a higher chance of Down's syndrome, Edwards' syndrome or Patau's syndrome, you may be offered further testing. Depending on the circumstances, this can include non-invasive prenatal testing (NIPT) or a diagnostic test such as CVS or amniocentesis. These tests answer different questions and have different benefits and limitations.

 

You don't have to decide what you would do with a higher-chance result before you've even had the screening. But it can be helpful to know that screening is the beginning of a decision-making pathway, rather than a single yes/no answer. If you are offered further testing, ask your maternity team to explain:

• What the test is looking for

• How accurate it is

• What the possible results are

• How quickly you might receive the result

• Whether the test carries any risks

• What your options would be depending on the result

 

You can then decide what information would be useful to you.

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The 20-week Screening Scan

 

Between 18 weeks and 20 weeks + 6 days, you'll usually be offered the 20-week screening scan. This is an ultrasound scan that looks in detail at your baby's physical development. The screening looks for 11 different physical conditions, including conditions affecting areas such as the baby's:

• Brain

• Face

• Heart

• Bones

• Spine

• Abdomen

• Kidneys 

 

The scan can also check the position of your placenta. Most scans will show that your baby appears to be developing as expected.

But, importantly, the scan cannot find every health condition. So again, screening provides information. It cannot provide a guarantee.

You can read more about this in [Ultrasound Scans].

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Is Screening Compulsory?

 

No. Screening during pregnancy is your choice. You can discuss the tests you're offered with your midwife or doctor and decide whether or not you want to have them. You can also change your mind. That doesn't mean there is a "right" answer. For some people, having as much information as possible feels reassuring. For others, they may decide that certain information would create more anxiety than reassurance, or that they wouldn't want further testing whatever the result. Some people may choose some screening tests and decline others. Your decision may also depend on your individual circumstances, beliefs, previous experiences and what you would want to do with the information. The important thing is that you understand what you're being offered well enough to make a decision that feels right for you.

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"But isn't Screening a Good Thing?"

 

Screening can be incredibly valuable. It can identify conditions earlier, allow appropriate care to be offered, help parents prepare for a baby's needs, and provide information that may influence decisions about pregnancy or treatment. But useful does not mean compulsory.

And choosing not to have a particular screening test doesn't mean that you don't care about your baby. Equally, choosing to have screening doesn't mean you're hoping for a particular result or that you're making a decision about your pregnancy. You are simply deciding what information you would like to have.

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Questions to ask before Agreeing to Screening

 

If you're unsure, these questions can help.

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"What exactly is this test looking for?"

Make sure you understand what condition or conditions are being screened for.

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"Is this a screening test or a diagnostic test?"

This is particularly useful when you're being offered further testing following a screening result.

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"What would the result tell me?"

Ask what information you'll actually receive.

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"How accurate is the test?"

No screening test is perfect, and understanding its limitations matters.

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"What happens if the result shows a higher chance?"

Knowing what might happen next can make the decision feel less overwhelming.

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"Would I be offered further testing?"

If so, ask what that would involve.

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"Do I have to decide today?"

Some decisions are time-sensitive, but it is still reasonable to ask whether you have time to think.

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"What would happen if I decided not to have this test?"

You are allowed to understand the alternative too.

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What if I Don't Know What I'd do With the Information?

 

This is a really important question. Sometimes people feel that they need to know "Would I continue the pregnancy?" before deciding whether to have screening. But there can be many reasons for wanting information. You might want to:

• Prepare emotionally

• Prepare practically

• Arrange specialist care

• Learn more about a possible condition

• Make decisions about where to give birth

• Understand what support might be available

• Simply know more about your baby's health

 

There isn't one correct reason to want information. And you don't necessarily have to know exactly what you would do with every possible result before deciding whether to have a screening test. If you're unsure, talk it through with your midwife or another appropriate healthcare professional.

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Screening can Bring up Big Feelings

 

It's completely understandable if screening feels exciting, reassuring, frightening or confusing. You may find yourself thinking: "What if something is wrong?" "What if I get a high-chance result?" "Would I want to know?" "What would I do with that information?" "What if I choose not to have the test and then something happens?" These aren't easy questions. If screening is making you particularly anxious, tell your maternity team. You don't have to navigate a difficult result or decision on your own.

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A Final Thought About Screening

 

Screening is about information, not certainty. A screening test can help identify whether you or your baby may have a higher chance of a particular condition. It cannot predict the future. And accepting or declining screening isn't a measure of how much you care about your baby. The most important thing is that you understand:

 

What is being offered.

What it can and can't tell you.

What might happen next.

And whether having that information feels right for you.

 

You don't need to have all the answers. You can ask questions. You can take time to think. And you can make your decision based on your own circumstances.

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Explore next

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[Understanding Screening Results]
Confused by your screening result? Learn what the numbers actually mean, what a higher or lower chance result tells you, and what might happen next.

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[Ultrasound Scans]
Find out what happens during pregnancy scans, what they're looking for, and what you can expect at each stage.

 

[Questions to Ask About Tests]
A practical list of questions to help you understand what you're being offered and make informed decisions about your care.