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Hopes raised of risk-free way to test for Down's syndrome

Doctors have developed a blood test for Down's syndrome that could eliminate the need for invasive investigations that put the unborn baby at risk.

Women at high risk of having a Down's syndrome baby traditionally have a series of scans and hormone level measurements to determine whether they need an invasive test, such as amniocentesis or chorionic villus sampling (CVS), in which a needle is inserted into the womb and a sample of fluid or tissue extracted.

The danger is that in 1 per cent of cases the invasive test causes a miscarriage and the loss of the baby. Up to one in 20 women have amniocentesis or CVS in the UK.

The DNA blood test developed by Professor Dennis Lo and colleagues from the Chinese University of Hong Kong successfully detected 86 women who were carrying Down's babies out of 753 who gave blood samples in Hong Kong, the UK and the Netherlands.

The study showed the test was highly accurate and did not miss any cases. It could mean that 98 per cent of invasive procedures could be avoided, the authors say in the British Medical Journal.

Down's syndrome occurs in around one in 800 births, and is more common in older mothers. The rate has soared by 71 per cent in the last 20 years as more women delay starting a family.

However, the number of babies born with Down's syndrome has remained fairly level at around 750 a year, although it has fluctuated from year to year by around 20 per cent.

Improvements in screening mean that more of the affected pregnancies are being detected earlier, and most now end in terminations.