Presentation: Fetus that is small for gestational age

A woman attends her 28-week community midwife appointment and is found to have a symphysis fundal height below the 10th centile on her customised growth chart. She is referred to secondary care for a fetal growth scan, at which it is confirmed that the fetus is on the first centile based on fetal biometry.

• Genomic testing should be discussed in cases in which there is significant growth restriction with no evidence of placental insufficiency or other suspected cause. Note: there remains a possibility of placental insufficiency and a co-existent genomic cause for small fetal size.
• Genomic testing should be discussed in cases in which small-for-gestational-age (SGA) is present alongside other fetal anomalies, or in which early pregnancy aneuploidy screening returned a high chance result.

• 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 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:
  • 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 other anomalies and the above testing is non-diagnostic, or fetal growth is significantly reduced (without evidence of placental insufficiency), 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 DNA-based tests (all the above listed tests), an EDTA sample 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
• Royal College of Obstetricians and Gynaecologists: Small-for-gestational-age fetus, investigation and management (Green-top Guideline No. 31)

For patients

• Royal College of Obstetricians and Gynaecologists: Having a small baby