Down Syndrome Screening: Complete Guide
Screening for Down's syndrome (trisomy 21) is a routine, optional part of NHS antenatal care, alongside screening for two related conditions, Edwards' syndrome and Patau's syndrome. It's offered to every pregnant woman, but it's entirely your choice whether to have it — there's no right or wrong answer, and your care won't change if you decline.
The screening options
- Combined screening is usually offered between around 11 and 14 weeks. It combines a blood test with measurements taken during your dating/nuchal translucency scan, alongside your age, to produce a personalised chance (rather than a yes/no answer) of the baby having one of these conditions.
- The quadruple test is offered later in pregnancy, generally between about 15 and 20 weeks, for women who missed the window for combined screening. It uses blood test results alone rather than a scan.
- Non-invasive prenatal testing (NIPT) analyses small fragments of the baby's DNA found in your blood. It's more accurate than combined or quadruple screening and is offered on the NHS to women whose combined or quadruple test shows a higher chance result, and is also available privately for anyone who wants it earlier or as a first-line option.
Understanding your result
It's important to know that all of these are screening tests, not diagnostic tests. They tell you whether your chance of the baby having Down's syndrome is higher or lower — they cannot confirm or rule it out with certainty. A "higher chance" result does not mean your baby definitely has the condition; most babies in this category do not.
- If your result comes back lower chance, no further testing is usually needed, though it doesn't guarantee the baby doesn't have the condition.
- If your result comes back higher chance, you'll be offered a conversation with a midwife or specialist, further information, and the choice of further testing.
- Diagnostic tests — chorionic villus sampling (CVS) or amniocentesis — are the only tests that can give a definite diagnosis, as they involve testing a small sample of cells from the pregnancy directly. These carry a small risk of miscarriage, so they're only offered after a higher chance screening result, and having one is always your choice.
Frequently Asked Questions
How accurate is Down's syndrome screening?
Combined screening and the quadruple test give a personalised chance rather than a certain answer, and NIPT is generally more accurate than either. None of these screening tests can diagnose Down's syndrome with total certainty — only a diagnostic test like CVS or amniocentesis can do that. Your midwife or screening service can talk you through the detection and false-positive rates for whichever test you're offered.
What happens if screening shows a higher chance result?
You'll be offered a discussion with a midwife or a specialist screening counsellor to talk through what the result means and your options. This usually includes the choice of NIPT (if you haven't already had it), or a diagnostic test such as CVS or amniocentesis. You're never obliged to have any further testing, and many women choose to continue with screening information alone.
Do I have to have Down's syndrome screening?
No, screening is entirely optional at every stage. You can decline the initial screening, or accept it but decline any further tests if you receive a higher chance result. Your midwife will support whatever decision you make and your routine antenatal care continues either way.
This article is for informational purposes only and does not constitute medical advice.
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