Singapore Straits Times 1st March 2001

Ultrasound scans used to detect whether a pregnant woman may give birth to a child with Down's syndrome are less accurate than believed

CHICAGO - Several features on ultrasound scans that doctors thought were warning signs of Down's syndrome are almost always harmless, leading many women with normal foetuses to undergo unnecessary amniocentesis, researchers say.

The analysis of 56 previous studies casts doubt on the reliability of ultrasound in detecting Down's syndrome in the womb.

Down's syndrome is caused by chromosomal abnormality.

Pregnant women routinely undergo blood tests and ultrasound scans to check for abnormalities.

When warning signs are seen on the ultrasound image, women are often advised to undergo amniocentesis in which a needle is used to draw fluid from the womb for analysis.

The procedure carries a small risk of causing a miscarriage.

In this latest research, doctors looked at seven markers sometimes seen on ultrasound scans that are thought to indicate an increased risk of Down's syndrome.

Only one of those markers - a shaded area suggesting a thickening at the back of the neck - was found to be a reliable enough indicator to justify an amnio, said Dr Rebecca Smith-Bindman, a radiologist at the University of California at San Francisco.

'Even then, only 3 per cent of foetuses will be affected by Down's syndrome, but this risk is sufficiently high that a woman might consider invasive testing with amniocentesis,' she said.

The six other markers were certain brain cysts, shortened thigh and upper-arm bones, bright spots on the bowel or heart and high fluid levels in the kidneys.

About 10 to 14 per cent of pregnant women have one of these markers, but fewer than 1 per cent have Down's babies, Dr Smith-Bindman said.

For women whose blood tests were normal, 'if your baby is found to have any of these isolated markers, your baby is almost certainly normal and you shouldn't be concerned about it and undergo an amnio because of it', she said.

In 1998, the latest year for which figures are available, 112,778 amnios and 2.5 million ultrasounds were performed in the United States.

Dr Smith-Bindman said 'clearly a lot' of the amnios were unnecessary. --AP