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Antenatal screening

Extracted from Survival Guide to Midwifery, 2nd Edition (2012) Diane M. Fraser and Margaret A. Cooper, Oxford; Churchill Livingstone: 2012. Courtesy Elsevier

Tests for fetal abnormality

There are two types of test for fetal abnormality

  • Screening tests
  • Diagnostic tests

Screening for fetal abnormality

Screening tests aim to identify a proportion of individuals who have the highest chance of a named disorder. This makes it possible to target further investigations towards those with the best indication. Women who undergo screening tests will be classified as above or below an action limit, whereby they are recalled and offered follow-up procedures.

Diagnosis for fetal abnormality

Diagnostic tests are performed to confirm or rule out the presence of a particular abnormality.

Before offering screening/diagnostic tests it is essential to obtain informed consent. The following should be discussed:

  • Purpose of the procedure
  • All risks and benefits to be reasonably expected
  • Details of future treatments that could arise as a consequence of testing
  • The option of refusing any tests
  • The offer to answer any queries

Ultrasound screening for fetal anomalies

Ultrasound screening for fetal anomalies should be routinely offered, normally between 18 weeks and 20 weeks 6 days. Guidance from the UK's National Institute for Health and Care Excellence (NICE) (2008) states, “At first contact with a healthcare professional, women should be given information about the purpose and implications of the anomaly scan to enable them to make an informed choice as to whether or not to have the scan: The purpose is to identify fetal anomalies and allow:

  • Reproductive choice (termination of pregnancy)
  • Parents to prepare (for any treatment/disability/palliative care/termination of pregnancy)
  • Managed birth in a specialist centre
  • Intrauterine therapy

If an anomaly is detected, the woman should be informed of the findings to enable them to make an informed choice about whether or not they wish to continue with the pregnancy or have a termination of pregnancy. The routine anomaly scan should include:

  • Fetal echocardiography (routine nuchal translucency screening for cardiac anomalies is not recommended)
  • Neural tube defects (alpha-fetoprotein testing not required) (NICE, 2008)

Screening for Down's syndrome

Should be performed by the end of the first trimester (13 weeks 6 days) but provision should be made for later screening (up to 20 weeks 0 days) for women booking later in pregnancy. (NICE, 2008) If a pregnant woman receives a screen-positive result for Down's syndrome, she should have rapid access to counselling by trained staff. (NICE, 2008)

The Practising Midwife featured article

Advancing maternal age and trisomy screening: the practice challenges of facilitating choice and gaining consent  Maria Birt The Practising Midwife December 2015, vol 15, issue 11 pp 11-15

Resources

National Institute for Health and Clinical Excellence (NICE) (2008) Antenatal care for uncomplicated pregnancies. Clinical guideline 62. https://www.nice.org.uk/guidance/cg62

 

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