Other Tests for Down’s Syndrome
What is a quadruple test?
This is a screening test where four biochemical markers are measures as opposed to three in the ‘Triple test’ and two in the ‘Double test’ as the names suggest. In addition to levels of AFP, beta-hCG and estriol, another marker called Inhibin-A is also measured. The quadruple test is claimed by some experts to have better detection rates than either the Double or the Triple tests.
As a general rule, in Down’s syndrome, levels of AFP and estriol tend to be low and those of free beta-hCG and Inhibin-A are raised.
The test is in use in some but not all hospitals in the UK.
What is an integrated test?
Several studies have been conducted to look at a more effective non-invasive screening test in pregnancy. It is now clear that the ‘integrated test’ is markedly superior to the standard Double or Triple tests.
The integrated test is done in two phases.
The first phase is done in the first trimester and involves an ultrasound scan and blood tests.
The USS measures the thickness of the back of the baby’s neck (nuchal translucency) and also confirms the precise gestation. The blood test measures the concentration of a chemical called pregnancy associated plasma protein A (PAPP-A).
The second phase involves a blood test where the levels of the following are measured:
Alpha-fetoprotein (AFP or αFP)
Free beta-hCG (β-hCG)
Unconjugated estriol (uE3)
Results from the two phases, together with maternal age are integrated to compute a risk for Down’s syndrome for that particular individual.
How effective is the ‘integrated test’?
This test will detect 8 to 9 out of ten pregnancies with Down’s Syndrome (The triple tests detects 6 out of 10). A positive integrated test is not diagnostic. It just gives the mother a chance to decide on whether to have a definitive diagnostic test i.e. a CVS or amniocentesis.
What proportion of pregnancies with a positive integrated test will actually be found to have affected babies?
About 10%. This means 9 out of 10 pregnancies with a positive integrated test result will have babies that are not actually affected.
The strength of the integrated test lies in the fact that it hardly misses an affected pregnancy detecting almost 90% of them.
Can the Integrated Test miss an affected pregnancy?
Yes. About 1 in 10 of affected pregnancies will be missed by the test. This means, it is still possible to have a baby affected by Down’s syndrome even after a negative test. However, the chances of this happening are markedly reduced when this test is used.
If I book late for my antenatal care, can I still have the Integrated Test?
No, this will not be possible as the required first phase has got to be done in the first trimester i.e. before 13 completed weeks of gestation.