Down syndrome screening Flashcards
what gestational age does a foetus need to be at before tests for DS can be performed?
> 11
what is the standard test for DS in the UK and at what gestational age is it performed?
the combined test
11 weeks to 13 + 6 weeks
3 aspects of the combined test
which results indicate DS?
nucal translucency (thickened)
b-HCG (raised)
PAPPA (low)
how will trisomy 13 and 18 present on the triple test?
similarly to DS but with an especially low PAPPA
2 tests which can be used to screen for DS if the pregnancy is beyond 13 + 6 weeks
the triple test
the quadruple test
at which gestational ages can the triple/quadruple tests be performed?
between 15 and 20 weeks (redundant after this?)
triple test (results indicating DS)
b-HCG (high)
AFP (low)
serum oestradiol (low)
quadruple test (results indicating DS)
b-HCG (high)
AFP (low)
serum oestradiol (low)
inhibin A (high)
how are the results of DS screening given? (i.e. what do they mean?)
they are expressed as a risk score - NB the mother’s age also contributes to this risk score
at what risk of DS is the mother offered an invasive screening?
any risk greater than 1 in 150
2 invasive tests for DS
when are they performed?
amniocentesis is performed from 15 to 20 weeks
CVS is performed from the time the risk is calculated to 15 weeks
an alternative to invasive testing for DS
NIPT (non-invasive prenatal testing) which is a maternal blood test used to measure foetal DNA from the placenta
