Our study suggests that examination of the fetal profile at 11 - 14 weeks could have major beneficial implications

Professor Kypros Nicolaides, Harris Birthright Centre

About one in 1,000 babies are born with Down's syndrome.

It is caused by the presence of an extra chromosome in a baby's cells.

Prenatal diagnosis of Down's syndrome involves the identification of three copies of chromosome 21, known as trisomy 21.

The methods currently available - based on age of mother, blood test, and nuchal translucency, which measures the build up of fluid at the back of the neck - are, if combined, 75% sensitive to the presence of Down's syndrome.

But some women have '"false-positive" results, and are therefore recommended for invasive tests unnecessarily.

Older mothers have a higher chance of having a baby with Down's syndrome, though age alone is the least accurate predictor.

If the nasal bone test was also used alongside age and the nuchal scan, the accuracy of prediction could increase to 85% or more, scientists say.

Miscarriage reduction

Professor Kypros Nicolaides, of London's Harris Birthright Research Centre for Fetal Medicine at Kings College Hospital School of Medicine, led the research.

The team looked at 700 foetuses aged between 11 and 14 weeks between January and October this year.

Research published in the Lancet indicated nasal bone was found to be absent in 73% of 59 foetuses later found to have Down's syndrome, and in just three (0.5%) of 603 chromosomally normal foetuses.

Foetuses without a nasal bone were estimated to be around 150 times more likely to have trisomy 21, compared with normal foetuses.

The test could help identify which children will have Down's syndrome more accurately

Professor Nicolaides said: "Our study suggests that examination of the fetal profile at 11 - 14 weeks could have major beneficial implications."

In addition to improving the accuracy of prediction to 85%, combining the nose test with maternal age and the nuchal translucency test could reduce the false-positive rate from 5% to 1%.

That, say the researchers, could mean a five-fold reduction in the rate of miscarriage from invasive testing.

Benefits

Professor Howard Cuckle, writing in the Lancet, said testing foetuses in the first trimester rather than the second had a number of benefits.

"These benefits include, for some, an early diagnosis with consequent safer and less traumatic therapeutic abortion, and, for most, an earlier reassurance."

He called on the Department of Health, which is developing a national Down's syndrome screening programme focusing on second trimester testing, to take note of this research.

A spokeswoman for the Down's Syndrome Association said it accepts that prenatal testing for Down's syndrome is now a routine part of ante-natal care.

She added: "However, we strongly believe that any programme of testing for a genetic condition must be accompanied by non-directive counselling. Individuals can then make a decision based on full and accurate information.

"Appropriate support must be provided regardless of the choices made."