Breakthrough in blood test ends risks to foetus

A revolutionary system for testing unborn babies for life-threatening diseases has been launched by British scientists. The technique - which is far safer than present methods for detecting conditions such as Down's Syndrome - reveals the health of foetuses from tiny fragments of their DNA that have leaked into their mothers' bloodstream.

As a result, doctors will no longer have to take samples directly from the womb for tests.

The breakthrough should prevent thousands of miscarriages when the screening system is introduced across the country in a few years, say scientists.

'At present, if doctors want to test a foetus to find out if it has Down's syndrome, or the blood disease thalassaemia, they have to stick a needle into the womb and remove tissue that surrounds the foetus,' said one of the project leaders, Professor Stan Urbaniak of Aberdeen University. 'Unfortunately that carries a small but significant risk of triggering a miscarriage and, given that these tests - such as amniocentesis - are given to tens of thousands of women every year, this causes hundreds of spontaneous abortions.'

Non-invasive pre-natal diagnosis (NIPD) is being used in trials in Aberdeen and Bristol to test for the potentially fatal haemolytic disease of the newborn (HDN), which occurs when a baby with rhesus-positive blood is born to a mother who is rhesus-negative.

During birth, a baby's blood often spills into its mother's bloodstream. This can trigger a reaction in her body that immunises her against rhesus-positive blood. Then, when she becomes pregnant again, if her new baby again turns out to be rhesus-positive, her immune defences attack the foetus. Hundreds of babies are affected every year, and until recently many died. 'We can do a great deal to help them now, but haemolytic disease can still kill,' said Urbaniak.

Testing to find if a foetus has rhesus-positive blood is therefore crucial in dealing with the disease. The miscarriages associated with invasive testing 'will not happen with the new technique', said Urbaniak.

Non-invasive pre-natal diagnosis exploits the fact that cells in a growing foetus are regularly replaced. The old ones die, break open and spill their genes into the mother's bloodstream, from which they can be retrieved. 'There are only minute fragments of foetal DNA in them,' said Urbaniak. 'But by using gene amplification we can create millionfold copies of the fragments, enough to be detected by special analytic techniques.'

It is this system that scientists introduced a few months ago in Aberdeen and Bristol, as part of a European project called Safe, or Special Advances in Foetal Evaluation. But they stress that further trials are needed to perfect the system. 'If a result shows a foetus has positive blood, we can be sure we need to take action. If the result is negative, we cannot be sure that we have not simply analysed the mother's DNA by mistake. In other words, we need some system of double checks to make sure of our accuracy, not just for haemolytic disease but for Down's, blood ailments like sickle-cell disease and other conditions,' he added.

'I am confident that in a few years we will be able to test the blood of the unborn without putting these babies at any risk whatsoever.'