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The Combined Screening Test in Pregnancy: What It Includes

The combined screening test is the most common first trimester screening offered on the NHS. It combines a blood test with an ultrasound measurement to estimate the chance of your baby having certain chromosomal conditions. This guide explains what the test includes, when it happens, and how to interpret the results.

Table of Contents

  1. What the Combined Test Includes
  2. When It Is Offered
  3. Understanding Your Result
  4. Next Steps After Screening
  5. FAQ

What the Combined Test Includes

The combined test has two parts. The first is a blood sample, usually taken from your arm, which measures two substances in your blood: pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG). The second is an ultrasound scan, performed through your abdomen, which measures the nuchal translucency (NT) — the fluid at the back of your baby's neck. Your age, weight, and the exact gestational age are also factored into the calculation.

When It Is Offered

The combined test is offered between 11 weeks and 14 weeks of pregnancy. It is usually performed at the same appointment as your dating scan, which is the first routine ultrasound on the NHS. If you miss this window, a second trimester blood test (the quadruple test) can be offered between 15 and 20 weeks, though it is slightly less accurate.

Understanding Your Result

Your result is given as a chance rather than a yes or no. For example, a result of 1 in 1,500 means that out of 1,500 women with the same result, one would have a baby with Down syndrome. In England, a result of 1 in 150 or higher risk (that is, a chance of 1 in 150 or less) is considered higher risk and is offered further testing. Most women receive a lower risk result, but lower risk does not mean zero risk.

Next Steps After Screening

If your result is lower risk, you continue with routine antenatal care. If your result is higher risk, you will be offered a non-invasive prenatal test (NIPT) or a diagnostic test such as chorionic villus sampling (CVS) or amniocentesis. You will also be offered counselling to help you decide. Screening is optional — you can decline all or part of it.

FAQ

### Does the combined test detect all conditions?

No. It screens for Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). It does not detect other genetic conditions or structural problems, which may be picked up at the 20-week scan.

Is the combined test safe for my baby?

Yes. Both the blood test and the ultrasound scan are completely non-invasive and carry no risk to your baby. Only follow-up diagnostic tests carry a small risk.

This article is for informational purposes only and does not constitute medical advice.

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