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Example clinical scenario

A primigravid (first-time pregnant) woman is referred to fetal medicine because she has just had her fetal anomaly ultrasound at 20 weeks’ gestation and, although the head circumference and the abdominal circumference plot onto the 50th centile, the femur length is on the first centile.

When to consider genomic testing

  • When the femur length in the second or third trimester is less than the first centile for gestational age.
  • When the femur length is disproportionately small compared with the head circumference and abdominal circumference.
  • When there are other anomalies noted on ultrasound other than short femur length.
  • When there are other bony anomalies seen on a scan (unusual head shape, small chest size, signs of bowing or fractures in the long bones – see Presentation: Pregnancy with suspicion of a skeletal dysplasia).
  • When there is no evidence of placental insufficiency.
  • When there is a higher-chance first- or second trimester screening result, or when the parents have previously declined screening but now wish to receive it.
  • When there is a family history of skeletal abnormalities or significant short stature (>3 standard deviations).

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.
  • Take a detailed history, which should include:
    • Family history of short stature.
    • Family history of skeletal problems.
    • Look carefully at both parents for height and disproportion.
  • Refer to local guidance regarding fetal medicine referral. Further review in a fetal medicine unit is usually warranted.
  • A fetal medicine review will determine whether genomic testing is appropriate and referral to clinical genetics will be considered.
  • Depending on the clinical scenario, a range of different genomic tests may be considered:
  • For many of the tests (particularly whole genome and exome sequencing), parental samples are also needed or are helpful.
  • For tests that are undertaken using whole genome sequencing (WGS), you will need to:
  • For tests that do not include WGS, you will need to:
    • complete a test order form and consent (record of discussion) form, available from your local Genomic Laboratory Hub (GLH).
    • include details of the phenotype in the test order form (refer to HPO terms or the clinical summary) as well as the appropriate panel name(s) with associated R number.
    • parental samples may be needed for interpretation of the proband’s result. Parental samples can be taken alongside that of the proband, and their DNA stored, or can be requested at a later date if needed.
  • All of the above tests are DNA based and an EDTA sample (purple-topped tube) is required.
  • 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.


For clinicians


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  • Last reviewed: 27/02/2024
  • Next review due: 27/02/2025
  • Authors: Dr Linden Stocker
  • Reviewers: Professor Sahar Mansour, Dr Jessica Woods