Skip to main content
Public beta This website is in public beta – please give your feedback.

Example clinical scenario

A pregnant woman presented for her first-trimester combined screening. During ultrasound, measurements of the fetal crown-rump length and fetal nuchal translucency were taken, while maternal serum PAPP-A and free beta-HCG measurements were obtained via laboratory tests. A statistical risk calculation was performed by clinical scientists to estimate the chance of Down syndrome (trisomy 21), or a joint chance for Edwards (trisomy 18) and Patau (trisomy 13) syndromes. Screening test results show that the woman is a ‘higher-chance’ (1-in-2 to 1-in-150 risk ratio) for the conditions. She asks if there are any other tests that can be carried out.

When to consider genomic testing

Consider genomic testing when:

  • there is a higher-chance (1-in-2 to 1-in-150 risk ratio) first-trimester combined screening result; or
  • findings characteristic of a common aneuploidy are made during an ultrasound scan.

What do you need to do?

  • Consult the National Genomic Test Directory. From this directory you can access the rare and inherited disease eligibility criteria for information about individual tests and their associated eligibility criteria. You can also access a spreadsheet of all available tests.
  • To find out which genes are included on different gene panels, see the NHS Genomic Medicine Service (GMS) Signed Off Panels Resource.
  • Refer to local and national NHS Fetal Anomaly Screening Programme guidance regarding first-trimester screening.
  • A further discussion with the screening co-ordinator or a fetal medicine midwife is usually warranted to discuss options around non-invasive prenatal testing (NIPT) or diagnostic tests as the technology can provide a more sensitive screening test for information and reproductive choice.
  • If anomalies are noted on the ultrasound scan, a referral to a fetal medicine unit is usually recommended for a detailed scan and a review to determine which genomic tests are appropriate.
  • Genetic referral is not routinely indicated for higher-chance first-trimester screening results. In the case of suspected anomalies, a referral to clinical genetics may be considered.
  • Depending on the clinical scenario, a range of different genomic tests may be considered, as outlined below.
    • Where there is an isolated higher-chance screening record:
      • R401 Common aneuploidy screening: this will process only a QF-PCR and should be requested in cases where the pregnant woman might have a diagnosis of aneuploidy (trisomy 21, 18 or 13).
    • Where there are concerns regarding an atypical phenotype, the following may be considered:
    • Where there are multiple or complex anomalies and/or above testing is non-diagnostic, (rapid) fetal exome sequencing may be considered:
  • NIPT is offered as part of an evaluative roll-out and is currently not part of the test directory. Contact your local screening midwife or fetal medicine team for information and support on testing.
  • For whole genome sequencing (WGS)-based tests, you will need to:
  • For tests that do not include WGS, you will need to:
    • complete a test order form and consent (RoD) form, available from your local Genomic Laboratory Hub (GLH); and
    • include details of the phenotype (refer to HPO terms or the clinical summary) as well as the appropriate panel name(s) with associated R number.
  • For all these tests, DNA can be extracted using amniocentesis, chorionic villus sample or cordocentesis (fetal blood sample). For many of the tests (particularly WGS and exome sequencing), parental samples are also needed.
  • Information about patient eligibility and test indications was correct at the time of writing. When requesting a test, please refer to the National Genomic Test Directory to confirm the right test for your patient.

Resources

For clinicians

References:

↑ Back to top
  • Last reviewed: 19/03/2024
  • Next review due: 19/03/2025
  • Authors: Dr Sophie Earle
  • Reviewers: Jo Hargrave, Donna Kirwan, Dr Jessica Woods