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In the first-trimester screening test, two biochemical markers are analysed and combined with maternal age and the nuchal translucency measurement to generate a combined result.

The biochemical markers are:

  • pregnancy-associated plasma protein-A (PAPP-A); and
  • free ꞵ-human chorionic gonadotropin (free ꞵhCG).

An accurate measurement of the fetal crown-rump length and the nuchal translucency is required, as well as a maternal venous blood sample. The measurements must be recorded on the test laboratory form that goes with the sample to the biochemistry lab.

Test outcomes

If the screening returns a low-chance result for Down syndrome, Edwards syndrome and Patau syndrome, no further action is required.

Where a higher-chance result is given (over 1-in-150), further assessment should be offered. This may include further ultrasound imaging in a specialist fetal medicine unit, non-invasive prenatal testing or diagnostic testing requiring chorionic villus sampling or amniocentesis.

For further information, see Presentation: Patient with higher-chance first-trimester combined screening result.


For clinicians


Tagged: Technologies

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  • Last reviewed: 24/03/2023
  • Next review due: 24/03/2025
  • Authors: Donna Kirwan
  • Reviewers: Dr Jessica Woods