Antenatal screening of Downs Flashcards
(16 cards)
What is Downs syndrome?
A condition caused by three copies of chromosome 21 and is also caused by trisomy 21 which gives dysmorphic features and many associated conditions.
Who is offered screening for Downs?
All women but it is the choice of the woman.
What does the screening involve?
Measurements from fetus using USS and combining those measurements with woman’s age and blood results to provide an indication of risk of Downs.
What is the combined test?
First line and most accurate screening test performed between 11 and 14 weeks and combines results from USS and maternal blood tests.
What exactly does the USS measure?
Nuchal translucency which is the thickness of the back of the neck of the fetus.
Downs syndrome is one cause of a nuchal thickness greater than 6mm.
What maternal blood tests are done?
Beta-human chorionic gonadotrophin - higher result indicates a greater risk.
Pregnancy-associated plasma protein A - lower result indicates a greater risk.
What is the triple test?
Performed between 14 and 20 weeks gestation and only involves maternal blood tests.
What blood tests are part of the triple test?
- Beta-HCG - higher result indicates greater risk.
- Alpha-fetoprotein - lower result indicates greater risk.
- Serum oestriol - lower result indicates a greater risk.
What is the quadruple test?
Performed between 14 and 20 weeks gestation.
Same as triple but maternal blood testing for inhibin-A which if higher, indicates a greater risk.
When is invasive testing offered?
When the risk of downs is greater than 1/150.
What are the risks of invasive testing?
Infection.
What blood results would be expected in Edwards?
Everything would be low, except for inhibin.
What do screening tests provide?
A risk score for the fetus having Downs.
When greater than 1 in 150, woman is offered amniocentesis or chorionic villus sampling.
What is chorionic villus sampling?
Involves an USS-guided biopsy of the placental tissue which is used when testing is done earlier in pregnancy (before 15 weeks).
What is amniocentesis?
USS-guided aspiration of amniotic fluid using a needle and syringe which is used later in pregnancy once there is enough amniotic fluid to make it safer to take a sample.
What is non-invasive prenatal testing?
Detects abnormalities in the fetus during pregnancy which involves a simple blood test from the mother.
Blood contains fragments of DNA, some which will come from placental tissue so represents fetal DNA and those fragments can be analysed to detect conditions such as Downs.
