A blood test undertaken between 10 to 14 weeks of pregnancy may be more effective in diagnosing Down syndrome and two other less common chromosomal abnormalities than standard non-invasive screening techniques, according to a multicenter study led by a University of Californian, San Francisco (UCSF) researcher. In the study, which followed pregnancy outcomes in close to 16,000 women, the cell-free DNA blood test resulted in correctly identifying all 38 fetuses with Down syndrome, a condition associated with cognitive impairments and an increased risk of several medical disorders. The diagnosis was confirmed by newborn exam, prenatal, or postnatal genetic analysis. The test focuses on the small percentage of fetal DNA found floating in a pregnant woman's blood. DNA is amplified with a molecular "photocopying" technique known as polymerase chain reaction (PCR), and sequenced so that comparisons can be made between relative amounts of each chromosome's DNA. A greater quantity of DNA is indicative of some chromosomal conditions, including Down syndrome, which is characterized by an extra copy of chromosome 21, one of the 23 pairs of chromosomes. When the same women underwent standard screening, 30 of the 38 fetuses with Down syndrome were flagged, according to the study published online on April 1, 2015, in the New England Journal of Medicine. The article title is “Cell-Free DNA Analysis for Noninvasive Examination of Trisomy.” The screening comprises a blood draw in which hormones and proteins associated with chromosomal defects are identified, together with an ultrasound of the nuchal fold fluid in the back of the neck, an excess of which is suggestive of Down syndrome.
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