Antenatal Screening Flashcards

1
Q

What is the purpose of screening?

A

to identify individuals at a higher risk of a disease or condition

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2
Q

What is the purpose of screening for chromosomal abnormalities during pregnancy?

A

to establish which women should receive more invasive tests to establish a definitive diagnosis

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3
Q

What is involved in the combined test?

When is it performed?

A
  • this is the most accurate screening test for Down’s syndrome
  • it is offered to all women between 11 and 14 weeks gestation
  • it involves USS and maternal blood tests

this is an OPT IN test

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4
Q

What is the role of USS in the combined test?

A
  • it measures the nuchal translucency
  • this is the thickness of the back of the neck of the foetus
  • Down’s syndrome causes nuchal thickness > 6mm
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5
Q

What maternal blood tests are included in the combined test?

A

beta-HCG:

  • higher result = greater risk

PAPP-A:

  • lower result = greater risk

beta-HCG = beta-human chorionic gonadotrophin

PAPP-A = pregnancy-associated plasma protein-A

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6
Q

What is done to screen for Down’s syndrome if the woman misses combined screening?

A
  • the triple or quadruple test can be performed between 14 to 20 weeks gestation
  • these involve blood tests ONLY
  • they are not as accurate as combined screening
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7
Q

What blood tests form part of the triple test?

A

beta-HCG:

  • higher result = greater risk

serum oestriol:

  • lower result = greater risk

alpha-fetoprotein (AFP):

  • lower result = greater risk
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8
Q

How is the quadruple test different to the triple test?

A
  • it is the same, but has an additional blood test
  • it also includes inhibin-A
  • higher result = greater risk
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9
Q

When is someone deemed high risk of Down’s syndrome after screening?

What additional test are they offered?

A
  • the screening tests provide a risk score for the foetus having the condition
  • if the risk is > 1 in 150, they are high risk
  • high risk women are offered amniocentesis or chronionic villus sampling (CVS)
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10
Q

How can CVS / amniocentesis give a definitive answer about Down’s syndrome?

A
  • they involve taking a sample of fetal cells
  • karyotyping can then be performed
  • this provides a definitive diagnosis
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11
Q

What is chorionic villus sampling (CVS) and when is it performed?

A
  • it involves an ultrasound-guided biopsy of placental tissue
  • performed when testing is earlier in the pregancy (before 15 weeks)
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12
Q

What is amniocentesis and when is is performed?

A
  • it involves ultrasound-guided aspiration of amniotic fluid using a needle & syringe
  • it is performed later in pregnancy (after 15 weeks) than CVS
  • there needs to be enough amniotic fluid present in order for it to be safe to sample
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13
Q

What is a new alternative that is being introduced in place of invasive testing for high risk mothers?

A

non-invasive prenatal testing (NIPT)

  • this is NOT diagnostic, but gives a very good indication as to if the fetus is affected
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14
Q

What is involved in NIPT?

A
  • a blood test is taken from the mother
  • this contains fragments of DNA
  • some DNA fragments come from placental tissue and represent fetal DNA
  • these can be analysed
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