Understanding Screening Results

What do they actually mean?

You've had your screening test. Now you've got the result. And perhaps you're staring at a number that looks something like 1 in 100, 1 in 500 or 1 in 10,000, wondering what on earth you're supposed to do with that information. Or perhaps you've been told you have a "higher chance" result and your brain has immediately jumped to: "Does this mean something is wrong with my baby?" Not necessarily.

Understanding the difference between a screening result and a diagnosis is really important. So let's unpack it.

A Screening Result is Not a Diagnosis

Screening tests estimate the chance that a particular condition may be present. They do not usually tell you whether your baby definitely has that condition. So if your screening result says your baby has a higher chance of Down's syndrome, Edwards' syndrome or Patau's syndrome, it does not mean your baby definitely has the condition. Equally, a lower-chance result does not completely rule a condition out.

This is because screening tests are not perfect. They can sometimes identify a higher chance when the condition isn't actually present, or give a lower-chance result when a condition is present. That's why the language matters. Screening asks: "How likely is this?" Diagnostic testing asks: "Is this actually present?"

What Does "Lower Chance" Mean?

If you receive a lower-chance result, you'll usually be given a number. For example: 1 in 300

This means that, based on the screening information, there is an estimated chance of around 1 in 300 that your baby has the condition being screened for. Another way of looking at it is that, statistically, around 299 out of 300 pregnancies with the same screening result would not be expected to be affected. A lower-chance result is reassuring, but it isn't a guarantee. It means the estimated chance is low enough that, in the NHS screening pathway, you won't usually be offered further testing for that condition.

What Does "Higher Chance" Mean?

A higher-chance result means that the screening has estimated a greater chance that your baby may have the condition. But this is the really important bit: A higher-chance result does not mean your baby definitely has the condition. The NHS specifically points this out because it is very easy to hear "higher chance" and interpret it as "positive". Most people who receive a higher-chance result will go on to have a baby who does not have Down's syndrome, Edwards' syndrome or Patau's syndrome.

A higher-chance result means: "This result suggests we should offer you more information and the opportunity for further testing." It does not mean: "We've found out that your baby has this condition."

Understanding the Numbers

This is where screening results can become particularly confusing. Imagine you are given a result of: 1 in 100 That means there is an estimated 1% chance of the condition. You could also think of it as: Out of 100 pregnancies with this particular result, around 1 would be expected to be affected and around 99 would not. Now imagine your result is: 1 in 1,000 That's an estimated 0.1% chance. So although both results contain the words "1 in", they represent very different probabilities.

And there is one slightly counterintuitive thing to remember: The smaller the second number, the higher the chance. So: 1 in 10 = higher chance 1 in 100 = lower chance than 1 in 10 1 in 1,000 = lower chance again It sounds backwards at first, but once you think of the number as a fraction of pregnancies, it makes sense.

Why can a Screening Test get it Wrong?

Because screening tests are designed to identify people who may have a higher chance of a condition. They aren't designed to provide certainty. A screening test can produce:

A false positive - The screening result suggests a higher chance, but the baby does not have the condition.

A false negative - The screening result suggests a lower chance, but the baby does have the condition.

Neither is a sign that anyone has done anything wrong. It's simply a limitation of screening. This is one reason why screening and diagnostic testing are different things.

So what happens after a higher-chance result?

If your screening result shows a higher chance of Down's syndrome, Edwards' syndrome or Patau's syndrome, you'll usually be offered an appointment to discuss the result and your options. Depending on the screening pathway and your individual circumstances, you may be offered:

NIPT

Non-invasive prenatal testing (NIPT) is another screening blood test. It is more accurate than the initial screening test, but it is still a screening test rather than a diagnostic test.

CVS or amniocentesis

These are diagnostic tests. They analyse genetic material from the pregnancy and can provide a much more definitive answer about whether certain conditions are present.

No further testing

You can also choose not to have further testing. There isn't an automatic requirement to continue through the testing pathway just because you have received a higher-chance screening result. Your maternity team should support you whatever you decide.

What is the Difference between NIPT and Diagnostic Testing?

This is worth understanding because these tests are sometimes talked about as though they're interchangeable. They aren't. NIPT is another screening test. It can give you a much more accurate estimate of the chance of certain chromosomal conditions, but it still cannot give the same level of certainty as a diagnostic test.

CVS and amniocentesis are diagnostic tests. They can be used to establish whether certain genetic or chromosomal conditions are present, although, like any medical test, they have limitations and cannot test for every possible condition. Diagnostic tests also involve a small risk of miscarriage, which is something you should be given information about before deciding whether to have one.

What if my 20-week Scan finds Something?

The 20-week scan is also a screening test, but it works differently from the blood-based screening for Down's syndrome, Edwards' syndrome and Patau's syndrome. It looks in detail at your baby's physical development and screens for 11 physical conditions.

If something unexpected is seen, you may be offered further scans, specialist appointments or diagnostic testing depending on what has been found. And again, an unexpected finding on a screening scan doesn't necessarily mean that something is definitely wrong.

Your maternity team should explain what they have seen, what it might mean and what happens next.

"Higher Chance" doesn't tell you Everything About your Baby

This is another really important point. A screening result is about the chance of a particular condition. It doesn't tell you:

Exactly how a condition might affect your baby
What your baby's life would be like
What support your baby might need
What your birth might look like
What your experience of parenthood would be
Everything about your baby's health

If a screening or diagnostic test suggests that your baby may have a particular condition, you should be offered further information about that specific condition and support to understand what it could mean for your family. You don't have to make assumptions about your baby's future based on a single number.

What Questions can I ask after Receiving a Result?

If you've received a result that you're worried about, it can be difficult to think clearly in the moment. You might find it helpful to write these questions down.

"Can you explain exactly what my result means?"

Don't be afraid to ask them to explain it in plain English.

"What is the actual chance?"

Ask for the number rather than relying only on phrases such as "higher chance" or "lower chance".

"Is this a screening result or a diagnosis?"

This is an especially important question if you're being offered further testing.

"How accurate is the test?"

Ask what the test can and cannot tell you.

"What are my options now?"

There may be more than one possible next step.

"What are the benefits and risks of each option?"

This is particularly important if you're considering diagnostic testing.

"Do I have to decide today?"

Ask whether the decision is time-sensitive and how much time you have to consider your options.

"Who can I speak to if I have more questions?"

You don't have to process everything during one appointment.

You don't have to make every Decision at once

One of the hardest things about receiving an unexpected result can be feeling as though suddenly everything has to be decided. It doesn't. You can take things one step at a time. You might choose to have the initial screening. Then decide whether you want NIPT.

Then decide whether you want diagnostic testing. Or you may decide not to have further testing. You can ask questions at each stage.

And you can ask for support while you're making those decisions. A decision made at one stage does not automatically commit you to every stage that follows.

What if I'm feeling Anxious about my result?

Waiting for results or receiving an unexpected result can bring up a huge range of emotions. You might feel frightened, numb, confused, angry, guilty, overwhelmed or completely unsure what you think. You might even feel guilty for feeling anxious about a baby you already love. There is no "correct" emotional response. If you're struggling, tell your midwife or maternity team. You can also ask about specialist support. Antenatal Results and Choices (ARC) is a UK charity offering information and support around antenatal screening, diagnosis and decisions following unexpected results. You don't have to navigate this information alone.

A Note About Statistics

Statistics can be incredibly useful. But they can also be surprisingly difficult to interpret when you're the person sitting in the room hearing them. A result like 1 in 100 can sound very different depending on how it is presented. That's why it is completely reasonable to ask your healthcare professional to explain the number in more than one way.

For example: "Can you tell me what that means as a percentage?" or: "If 100 people had this same result, roughly how many would be expected to have the condition?" You are not being difficult by asking. You are making sure you understand the information you're being given.

The Most Important Things to Remember

If you take nothing else away from this page, remember these five things:

1. Screening is about chance

It does not usually give you a definite diagnosis.

2. A higher-chance result does not mean your baby definitely has the condition

It means the screening has identified a higher estimated chance.

3. A lower-chance result does not completely rule a condition out

Screening tests have limitations.

4. You may have options about what happens next

Depending on your result, you may be offered further screening, diagnostic testing or no further testing.

5. You can ask questions before making decisions

You don't need to understand everything immediately.

You are Allowed to Ask for Clarity

Pregnancy can sometimes feel like being handed a series of numbers, percentages and medical terms and being expected to know what to do with them. You aren't. If you've been given a screening result and you're not sure what it means, ask.

Ask what the number means.

Ask how likely the condition actually is.

Ask what the test can and can't tell you.

Ask what your options are.

Ask what happens if you do nothing.

And if you still don't understand, ask again.

Understanding your result is an important part of making an informed decision about what happens next.

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