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Monday, 16 August, 1999, 10:53 GMT 11:53 UK
Test cuts Down's syndrome false alarms

A safer test for Down's Syndrome has been developed
A safer, more accurate test for Down's syndrome could radically reduce the number of women who are wrongly told that their baby is at risk of having the condition, say US scientists.

But the new tests cannot be completed until around the fifth month of pregnancy, meaning women could face the trauma of abortion at a later stage when the foetus is more developed.

In the UK, women are currently offered a blood test around the third to fourth month of pregnancy.

This measures a combination of factors, including proteins. Low levels of some proteins have been associated with Down's syndrome.

Doctors emphasise that the tests only show the potential for risk, although improvements and the addition of ultrasound scans mean they might be up to 80% accurate.

If women come into a high risk category, they are offered a more invasive procedure - usually amniocentesis.

This test, which involves a needle drawing fluid from the womb, shows chromosomal abnormalities associated with Down's syndrome.

The new test, developed by researchers at the Wolfson Institute of Preventative Medicine in London, and reported in the New England Journal of Medicine, is said to identify 85% of Down's syndrome babies, and to have a 1% "false positive" rate, much lower than the traditional screening rate.

Reduced need for risky test

Because it is more accurate, the scientists say it could reduce by as much as four-fifths the need for invasive procedures which carry a risk of miscarriage.

Amniocentesis has a 1% risk of miscarriage, although this is reduced depending on the experience of the doctor carrying out the procedure.

And chorionic-villus sampling, in which tissue is taken from the placenta, carries a slightly higher risk, but results are available sooner than for amniocentesis.


An estimated two babies a week are born with Down's Syndrome in the UK
In England and Wales, invasive procedures result in around 280 miscarriages a year.

The US research involves screening in both the first and second trimester of pregnancy and integrating the results.

Some involved blood analysis, and others used ultrasound.

The main drawback is tha test results are unlikely to be available until around the 20th week of pregnancy, a few weeks later than for traditional blood screening.

In an editiorial in the New England Journal of Medicine, scientists from the Yale University School of Medicine say they believe this time lapse will mean the new test "is unlikely to gain wide acceptance in the United States".

But the Wolfson researchers say: "The fact that the results would not be available for an additional few weeks may be seen as a disadvantage, but any such disadvantage is outweighed by the substantial increase in safety."

Although the legal limit for abortion of a normal foetus is 24 weeks, a Down's syndrome baby is classed as having the potential for severe mental or physical abnormality and can legally be aborted at any time during pregnancy.

Ann Furedi of the British Pregnancy Advisory Service said: "Anything that improves the accuracy or safety of ante-natal tests is a good thing."

However, a spokesman for the Down's Syndrome Association said it was concerned that parents given test results indicating the condition were not given enough counselling about their options.

She said: "We are realistic about pre-natal screening for Down's syndrome - people are going to want to take advantage if it's more accurate.

"The difficulty we have is that we don't feel that tests are accompanied by adequate support."

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See also:

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26 Mar 99 | Health
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