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New antenatal blood test for Down's syndrome looks promising

BMJ 2007; 334 doi: http://dx.doi.org/10.1136/bmj.334.7590.391-a (Published 22 February 2007) Cite this as: BMJ 2007;334:391

Antenatal screening for Down's syndrome has come a long way since late amniocentesis was an older woman's only option. But the search continues for a simple blood test that can tell a woman in early pregnancy whether her baby has trisomy 21. Researchers are currently focusing on the fetal DNA found in maternal blood. One emerging technique uses single mutation polymorphisms to distinguish fetal DNA from maternal DNA, and researchers from the US recently used it to count the number of fetal chromosomes in blood samples from 60 women. Eight of the women were tested in the first trimester.

Three women had fetuses with trisomy 21. The new blood test picked up two of them, giving a sensitivity and a positive predictive value of 66.7%. A third woman had a false positive blood test result, and a fourth had a false negative one. The test's specificity and negative predictive value were both 98.2%. Overall, the test was about as accurate as current serum screening tests, although these results must be considered preliminary. We can be cautiously optimistic that this avenue of inquiry will eventually come up with an accurate and non-invasive test for Down's syndrome, says an accompanying editorial (pp 440-2). But we are not there yet.

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