Presentation: Fetus with an ultrasound phenotype suggestive of chromosomal anomalies

A couple attend their routine anomaly scan, having previously declined combined screening in the first trimester. There are several fetal anomalies detected during this scan, and the couple are referred to fetal medicine. At this appointment, it is confirmed that the fetus has a ‘strawberry-shaped’ cranium, choroid plexus cysts, an exomphalos and overlapping fingers. A diagnosis of trisomy 18 (Edwards syndrome) is suspected.

• Testing should be offered if there is a fetal phenotype suggestive of a chromosomal anomaly.
• The most common chromosome aneuploidies are:
  • trisomy 13;
  • trisomy 18;
  • trisomy 21;
  • Turner syndrome; and
  • triploidy.
• If there are fetal ultrasound anomalies that do not appear characteristic of the above common aneuploidies, please refer to one of the following alternative GeNotes articles (depending on the individual case):
  • Presentation: Patient has fetal anomalies discovered during their mid-trimester anomaly scan.
  • Presentation: Fetus with an isolated congenital anomaly.

• Refer to local guidance regarding fetal medicine referral. Further review in a fetal medicine unit is usually warranted.
• Genetic referral is not routinely indicated for atypical first-trimester screening risk. A fetal medicine review will determine which genomic testing is appropriate, and referral to clinical genetics can be considered in certain circumstances.
• The relevant team will refer to the NHS England National Genomic Test Directory eligibility criteria to determine which tests are available to your patient. The directory itself provides a list of all available tests.
  • For those working within NHS Wales, please consult the All Wales Medical Genomics Service website for information on how to arrange testing.
• Depending on the clinical scenario, a range of different genomic tests may be considered.
  • Where there are concerns regarding an atypical phenotype, the following may be considered:
    • R22 Fetus with a likely chromosomal anomaly. This will process both:
      • R22.1 Genome-wide common aneuploidy testing; and
      • R22.2 Chromosomal microarray.
    • Where there are multiple or complex anomalies and/or above testing is non-diagnostic, fetal exome sequencing may be considered:
      • R21 Fetal anomalies with a likely genetic cause: fetal exome sequencing.
        • Referral to clinical genetics and/or multi-disciplinary discussion is required.
        • A record of discussion form is required.
  • For all these tests, an amniocentesis or chorionic villus sample or fetal blood sample (in an EDTA tube) is required. For many of the tests (particularly whole genome and exome sequencing), parental samples are also needed or are helpful. Please refer to your local Genomic Laboratory Hub for details of test request forms and where to send samples.
• 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

• Fetal Medicine Foundation: Chromosomal defects
• NHS England: National Genomic Test Directory

For patients

• Down’s Syndrome Association
• SOFT UK (Patau and Edwards support)
• Turner Syndrome Support Society