Downs Syndrome Screening Flashcards
Down’s syndrome
Trisomy 21
Gives dysmorphic features
Purpose of Down’s syndrome screening
Decide which women should receive more invasive tests to establish a definitive diagnosis
What does a Down’s syndrome screening include
USS measurements from the fetus - nuchal translucency
Mother’s age and blood results:
- beta-HCG– a higher result indicates a greater risk
- Pregnancy‑associated plasma protein‑A (PAPPA) – a lower result indicates a greater risk
Combined Test
First line and the most accurate screening test
Performed between 11 and 14 weeks gestation
Ultrasound - nuchal translucency
Maternal blood tests
Nuchal translucency
Nuchal thickness > 6mm - higher risk of Down’s syndrome
Beta HCG
Higher result indicates a greater risk
Pregnancy‑associated plasma protein‑A (PAPPA)
Lower result indicates a greater risk
Triple Test
Between 14 and 20 weeks gestation.
Maternal blood tests:
Beta-HCG – a higher result indicates greater risk
Alpha-fetoprotein (AFP) – a lower result indicates a greater risk
Serum oestriol (female sex hormone) – a lower result indicates a greater risk
When is a combined test performed
11 - 14 weeks
When is a triple test performed
If a combined test has not been performed
14 - 20 weeks
When is a Quadruple Test performed
14 - 20 weeks gestation
What does a quadruple test involve
Beta-HCG – a higher result indicates greater risk
Alpha-fetoprotein (AFP) – a lower result indicates a greater risk
Serum oestriol (female sex hormone) – a lower result indicates a greater risk
Inhibin - A - a higher inhibin A indicates a greater risk
Antenatal Down’s syndrome screening risk implications
When the risk of Down’s is greater than 1 in 150 the woman is offered amniocentesis or chorionic villus sampling
Chorionic villus sampling (CVS)
USS - guided biopsy of the placental tissue.
When is chorionic villus sampling used?
When testing is done earlier in pregnancy (before 15 weeks)
Amniocentesis
USS - guided aspiration of amniotic fluid using a needle and syringe
When is amniocentesis used
Used later in pregnancy once there is enough amniotic fluid to make it safer to take a sample
Non-Invasive Prenatal Testing
Blood test from the mother.
Blood contains some fragments of placental tissue and represent the fetal DNA.
These fragments can be analysed to detect conditions such as Down’s but not definitive
