A BLOOD test could identify fetal genetic disorders like Down鈥檚 syndrome without invasive tests that raise the risk of miscarriage.
The test exploits the fact that after about five weeks of pregnancy a fetus begins to shed cells into its mother鈥檚 bloodstream, where they release fetal DNA. Analysing this DNA could reveal whether the baby will have birth defects, but it has proved difficult to isolate enough fetal DNA because the mother鈥檚 cells also tend to rupture once blood samples are taken.
To prevent this, Ravinder Dhallan at gene testing firm Ravgen in Columbia, Maryland, and his colleagues added formaldehyde to blood samples before isolating the DNA, raising the proportion of fetal DNA from around 7 per cent to 20 per cent. Variations in the precise code of the DNA enabled them to distinguish maternal from fetal DNA, which they could then scan for abnormal numbers of chromosomes, such as trisomy 21, which gives rise to Down鈥檚.
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In a preliminary study of 60 women, Dhallan鈥檚 team correctly identified chromosome numbers in 58 fetuses, including two cases of trisomy 21. However, one such case was not spotted, and one fetus was wrongly identified as having the disorder (The Lancet, DOI: 10.1016/S0140-6736(07)60115-9).
