2008/10/06
Invasive procedures currently used risk miscarriage and damage to the foetus.
A Stanford University test of DNA evidence in 18 pregnant women's blood correctly identified nine cases of Down's syndrome, reports PNAS journal.
The university now wants a larger-scale test. Babies with Down's syndrome have an extra copy of chromosome 21, causing physical and intellectual impairments.
If a foetus has three copies of chromosome 21 rather than the normal two, there will also be a relative increase in the quantity of chromosome 21 in the mother's blood because DNA can cross the placenta from the baby to the mother.
The "shotgun sequencing test" identifies and counts these fragments of DNA and is sensitive enough to detect the very small increase in amount of chromosome 21.
The new test correctly identified all the chromosomal abnormalities in a specially selected sample of 18 pregnant women - nine cases of Down's syndrome and two other inherited disorders or aneuploides caused by an abnormal number of chromosomes.
Dr Stephen Quake and his Stanford team say they need to repeat their study in a larger number of women, but they are confident that it could be used routinely in hospitals a few years from now.
Dr Quake said: "Non-invasive testing will be much safer than current approaches."
One of the current ways of confirming the syndrome is amniocentesis, in which a needle is used to take a sample of the fluid within the womb.
Approximately one in 100 women who have the test will miscarry as a result, according to the Royal College of Obstetricians and Gynaecologists.
A similar invasive procedure that takes a tissue sample from inside the womb, called chorionic villus sampling, carries a miscarriage risk of two in 100. It can be carried out at an early stage of pregnancy than amniocentesis - after 10 weeks gestation compared with after 15 weeks for amniocentesis.
Dr Quake said the new DNA test could be carried out at an even earlier stage of pregnancy than the current tests, giving women more time to make choices about their pregnancy.
Dr Lyn Chitty, an expert in genetics and foetal medicine at University College London Hospital, said: "This is a potentially exciting development which may take us closer to a safer, non-invasive test for Down's syndrome and the other major aneuploidies, trisomies 13 and 18."
Story from BBC NEWS
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