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A new blood test could tell a pregnant woman if her unborn child has Down’s syndrome, scientists say.

The technique, tested at Stanford University in the United States, is designed to look for tell-tale chromosome fragments in a blood sample.

During the Stanford tests, scientists were able to pinpoint signs of chromosomal abnormality in 18 pregnant women and correctly identied nine cases of Down's syndrome, the Proceedings of the National Academy of Sciences journal reports.

The university now wants conduct larger-scale trials for the test, which also picked up two other inherited disorders or aneuploides caused by an abnormal number of chromosomes.

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.

Last year the US company Ravgen Inc. announced the successful trial of a similar detection method.

At present a procedure called amniocentesis is used to test for chromosomal abnormalities. This involves inserting a long needle through the mother’s abdomen and drawing off fluid from the womb. As well as being uncomfortable and inconvenient, amniocentesis carries a small risk of miscarriage or infection.

Approximately one in 100 women who have the test will miscarry as a result, according to the Royal College of Obstetricians and Gynaecologists.

Professor Stephen Quake, who led the new study at Stanford, said that 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.

“Non-invasive testing will be much safer than current approaches," he said. "The earlier you know you’ve got a foetus with Down syndrome, the better able you are to prepare."

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."

Other scientists are looking to find different genetic markers in maternal blood for Down's. However, these tests would not work in all women, unlike the DNA test.

Carol Boys, chief executive of the Down's Syndrome Association, said: "There is no question that these non-invasive tests will be introduced in the next few years.

"It's therefore incredibly important that potential parents are given accurate information on Down's syndrome before they make a choice about whether to terminate or not.

"We don't consider Down's syndrome a reason for termination, but we recognise that bringing up a child with Down's syndrome isn't right for everyone.

"The more informed parents are, the better the position they are in to make the choice that is right for them."

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