Screening tests in pregnancy Flashcards
What is the combined screening test?
Tests for nuchal translucency & 2 serum markers
Human chorionic gondaotrophin (hCG)
Pregnancy associated protein A (PAPP-A)
Who is the CST recommended for?
Those booking in the 1st trimester
When can the CST be performed?
10-13/40 weeks
What are the advantages of the CST?
Early result
Detection rate = 85% - close to NHS target (90%)
False positive rate = 2.2% - close to NHS target (2%)
When is the quadruple test offered?
14-20/40 weeks
What does the quadruple test test for?
alpha-foetoprotein (AFP)
human chorionic gondatropin (hCG)
unconjugated oestriol
inhibin A
Is nuchal translucency tested in the quadruple test?
No - NT not reliable at this stage
The serum testing is combined with what to assess individualised risk?
The maternal age
How effective is the quadruple test?
Poorer test than CST
Detection rate = 80%
and a higher false positive rate = 3.5%
What is the risk threshold for a “positive” result from a CST?
1 in 150 or greater
How many have an affected foetus after a positive CST?
1 in 9 turn out to have an affected foetus
8 false positives for every 1 true positive
What are screen positive women offered?
Chorionic villus sampling (CVS) - placenta sample
Amniocentesis - amniotic fluid sample
When can CVS be performed?
11-14/40 weeks but miscarriage rate is 1-2%
When can amniocentesis be performed?
from 15 weeks but miscarriage rate is lower at 0.5-1%
What does non-invasive prenatal testing test for?
Circulating free foetal DNA in maternal circulation
