Prenatal screening tests

 

  1. Types of prenatal screening tests include:
  2. Ultrasound scanning
  3. Combined first trimester screening
  4. Second trimester maternal serum screening
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Important considerations about prenatal screening tests

  1. Screening tests can determine who is at increased risk of having a baby with Down syndrome. Women choosing screening tests should be informed that they will be offered further testing if they have an increased risk and that they may choose to proceed to diagnostic testing. Reasons for not having diagnostic testing include concern about the risk of miscarriage, not wishing to know prior to the birth, and termination of pregnancy being unacceptable to the family.
  2. Screening tests are non-invasive so there is no increased risk of miscarriage from the procedure.
  3. Every screening test has a ‘false positive’ rate, where women receive an increased risk result even though their baby is unaffected. This rate is usually around 5%.
  4. In the majority of pregnancies with an increased risk result on a screening test, the baby is unaffected. A common misconception held by women is that screening tests ‘show’ that the fetus has Down syndrome. Anxiety at any increased risk result is normal (see, Genetics in practice).
  5. Low risk results do not exclude Down syndrome or other abnormalities.
  6. A second trimester ultrasound may detect some birth defects but is not recommended as a screening test for Down syndrome.
  7. Neural tube defects and some other conditions may also be detected with second trimester maternal serum screening.
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