King’s College team develops more reliable test for Down’s syndrome

A new test, developed by King's College, London, can reliably tell if an unborn baby has Down's syndrome without putting it at risk.

All pregnant women are being offered screening for Down's syndrome, but the current screening test had a false positive rate (that is, the results suggested a problem when the foetus was in fact healthy) of around 3-4 per cent.

This meant, women were being exposed to needless risk through invasive testing, using chorionic villus sampling (CVS) or amniocentesis, with both procedures carrying around a one in 100 risk of causing a miscarriage.

If the false positive rate of the screening test could be lowered it would cut the number of women who needed invasive testing, resulting in fewer miscarriages.

The new screening technique involves carrying out an analysis of the small amounts of foetal DNA present in the mother's blood stream.

Tests on 1,005 women, had shown the new technique had a much lower false positive rate (around 0.1 per cent), meaning many fewer normal pregnancies had an unnecessary invasive diagnostic test with the new test. In around 2 per cent of women the new test showed no result, meaning that the conventional screening technique had to be used.

According to The King's College London team behind it, the test could help women decide if they needed further, invasive tests.

Around 750 babies born in the UK each year are afflicted with the condition.

The presence of an extra copy of chromosome 21, which occurs by chance, is responsible for the condition.

Women are currently tested between weeks 11 and 13 of pregnancy with an ultrasound measuring, a pocket of fluid at the back of a baby's neck - the nuchal translucency. Babies with Down's syndrome tend to have higher than normal levels of  fluid.

High risk women have the option for an invasive diagnostic test that would tell them if their baby had Down's.

Women also need to take a blood test to check for abnormal levels of certain proteins and hormones.

According to professor Kypros Nicolaides, who is leading the research and who also developed the nuchal fold test, the foetal DNA (cfDNA) test was much more definitive.