Presentation: Fetus with anomalies discovered during the mid-trimester anomaly scan

A couple attend their routine anomaly scan, having previously declined combined screening in the first trimester with an otherwise normal dating scan. The fetus is found to have severe ventriculomegaly, with a measurement of 16 millimetres.

If fetal anomalies are detected at the mid-trimester scan, referral to fetal medicine should be made and genomic testing should be discussed and offered in most situations.

The type of tests offered will depend on the suspected underlying cause and on the fetal phenotype.

• Refer to local guidance regarding fetal medicine referral. Further review in a fetal medicine unit is usually warranted.
• The fetal medicine review will determine whether genomic testing is appropriate and referral to clinical genetics will be considered.
• The clinical genetics team will review 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.
• The fetal medicine team will decide which testing is most suitable for the patient and/or discuss the case with a multi-disciplinary team, depending on the specific clinical scenario and the patient’s wishes.
• Depending on the clinical scenario, a range of different genomic tests 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, 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

• NHS England: National Genomic Test Directory
• NHS: Rapid exome sequencing service for fetal anomalies testing: FAQs
• Fetal Medicine Foundation: Ventriculomegaly
• Office for Health Improvement and Disparities: 20-week screening scan pathway requirements specification

References:

• Navaratnam K and Alfirevic K (Royal College of Obstetricians and Gynaecologists). ‘Amniocentesis and chorionic villus sampling.’ British Journal of Obstetrics and Gynaecology 2021: volume 129, issue 1, pages e1–e5. DOI: 10.1111/1471-0528.16821

For patients

• Antenatal Results and Choices: Genetic tests in pregnancy
• NHS: If antenatal screening tests find something
• Public Health England: Screening in pregnancy: 20-week screening scan
• Public Health England: Screening in pregnancy: CVS and amniocentesis information for parents