Combined Test in Pregnancy: Complete Guide
The combined test is the standard first trimester screening offered to everyone on the NHS, usually alongside the 12-week scan. It doesn't diagnose anything on its own — instead, it estimates your individual chance of your baby having Down's syndrome (trisomy 21), Edwards' syndrome (trisomy 18), or Patau's syndrome (trisomy 13), so you can decide whether you want further testing.
What the test actually involves
The combined test brings together three pieces of information to calculate a single risk figure:
- Nuchal translucency (NT) measurement — an ultrasound measurement of the fluid at the back of your baby's neck, taken between 11 weeks 2 days and 14 weeks 1 day
- A blood test — measuring levels of hCG and PAPP-A (pregnancy-associated plasma protein A), usually taken on the same day
- Your personal factors — including your age, weight, and how many weeks pregnant you are, since these all affect the baseline risk calculation
These three factors are combined into an algorithm that produces a single result, expressed as a chance, such as 1 in 500 or 1 in 2,000.
Understanding your result
Results come back as either lower-chance or higher-chance:
- A lower-chance result means your calculated risk falls below the national screening threshold — no further testing is needed, though it doesn't rule out a chromosomal condition completely
- A higher-chance result means your risk sits above the threshold — you'll be offered a conversation with a specialist midwife about further options, which may include non-invasive prenatal testing (NIPT) or a diagnostic test such as CVS or amniocentesis
It's worth remembering that a higher-chance result is not a diagnosis. Most people who receive a higher-chance result go on to have a baby without any of the screened conditions. The test exists purely to help you decide whether you want more information.
Making your decision
Screening for these conditions is entirely optional, and there's no right or wrong choice. Some parents want as much information as possible as early as possible; others prefer not to test at all, and both are valid decisions. Your midwife will talk you through what the test can and can't tell you at your booking appointment, giving you time to ask questions before you decide whether to opt in.
If your dates mean you've missed the window for the combined test, a quadruple test is available later in the second trimester as an alternative screening option, though it screens for fewer conditions.
Frequently Asked Questions
What does the combined test check for?
It screens for Down's syndrome, Edwards' syndrome, and Patau's syndrome by combining an NT ultrasound measurement, a blood test for hCG and PAPP-A, and your personal details such as age. It produces a single chance-based result rather than a yes/no diagnosis.
Is the combined test mandatory?
No. All screening in pregnancy, including the combined test, is entirely optional. You can decline it, accept only part of it (such as the scan but not the blood test), or ask for more information before deciding — your midwife will support whichever choice you make.
What happens if I get a higher-chance result?
You'll be offered an appointment with a specialist midwife to talk through your options, which typically include NIPT (a further blood test that's more accurate but still not diagnostic) or a diagnostic test like CVS or amniocentesis. There's no obligation to have any further testing if you'd rather not.
This article is for informational purposes only and does not constitute medical advice.
Related articles: