Safer prenatal test developed for Down's syndrome a step closer

Doctors have taken an important step closer to developing a test for Down's syndrome in pregnancy which would avoid posing a risk to the developing foetus.

Doctors have taken an important step closer to developing a test for Down's syndrome in pregnancy which would avoid posing a risk to the developing foetus.

Research to be published in The Lancet on Friday shows that a new technique based on detecting traces of foetal DNA present in maternal blood successfully identified Down's syndrome babies in three mothers on whom it was tried.

Current techniques for detecting Down's syndrome rely on blood tests, which give only a general indication of risk, followed by amniocentesis, performed after the 16th week of pregnancy. This involves inserting a needle through the abdomen into the womb to extract a sample of amniotic fluid, in which the foetus lies.

The procedure carries a 1 per cent risk of causing a miscarriage and, if positive, means parents have to make a decision about termination at a late stage of the pregnancy.

The new test has been developed by Dr Leo Poon and colleagues of the Chinese University of Hong Kong. They investigated the use of the Fish technique (fluorescence in situ hybridisation) to detect abnormalities of the baby's DNA. Since some foetal DNA is present in the mother's plasma, the technique can be applied to the mother's plasma samples, without need to take tissue from the womb or fluid from around the fetus.

The researchers said: "Ultimately, with further technical refinements, prenatal diagnosis by maternal plasma DNA analysis could reduce our reliance on invasive methods, leading to safer investigative protocols for mother and foetus."

They researchers said that large-scale trials should be carried out to assess the accuracy of the method.

The findings were released early by The Lancet, which normally strictly adheres to a Friday morning embargo on the contents of the journal, after it learnt that the Daily Express intended to publish them.