Presentation: Fetus with an ultrasound features suggestive of a chromosomal syndrome

A pregnant woman attends for the 20-week screening scan appointment, having previously declined first trimester combined screening. The sonographer identifies several fetal anomalies and the couple are referred to a fetal medicine specialist. The specialist confirms that the fetus has a ‘strawberry-shaped’ cranium, choroid plexus cysts, exomphalos and overlapping fingers. A provisional diagnosis of trisomy 18 (Edwards syndrome) is given.

• Testing should be offered if there is a fetal phenotype suggestive of a chromosomal anomaly or syndrome.
• The most common chromosome aneuploidies are, in order of prevalence:
  • trisomy 21 (Down syndrome);
  • trisomy 18 (Edwards syndrome);
  • trisomy 13 (Patau syndrome);
  • 45,X (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: Pregnant woman with fetal anomalies identified during 20-week screening scan; or
  • 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. A fetal medicine review will determine which genomic test is appropriate, and referral to clinical genetics can be considered if relevant.
• The requesting clinician will refer to the NHS England National Genomic Test Directory eligibility criteria to determine which, out of the list of tests available, is relevant for the clinical scenario and phenotype.
  • For information about how to arrange testing in Wales, Scotland or Northern Ireland, see our dedicated Knowledge Hub resource.
• Where there are concerns regarding an atypical phenotype, the following may be considered:
  • R22 Fetus with a likely chromosomal abnormality: 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, rapid fetal exome sequencing may be considered:
  • R21 Fetal anomalies with a likely genetic cause.
• All the above indications require a completed record of discussion form to process genomic samples.
• Invasive tests that can be undertaken include amniocentesis and chorionic villus sample (CVS). 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 (GLH) for relevant test request forms, collection tubes and advice on how and where to send genomic samples. It is important to contact the GLH in advance of any testing.
• 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
• Gov.uk: 11 physical conditions (20-week scan)
• Gov.uk: 20-week screening scan
• RCOG: Amniocentesis and Chorionic Villus Sampling (Green-top Guideline No. 8)

For patients

• Down’s Syndrome Association
• Gov.uk: Screening in pregnancy: CVS and amniocentesis information for parents
• Support Organisation for Trisomy 13 & 18 UK (Patau and Edwards support)
• Turner Syndrome Support Society