midwifeA blood test in pregnancy that can detect whether the developing foetus has Down’s syndrome is to be trialled at Great Ormond Street Hospital.

The test could significantly reduce the number of women who would need an invasive test to determine this, which can cause miscarriage.

This study will assess how and when the test could be introduced across the NHS. It is already available privately.

In the UK, 750 babies are born with Down's syndrome each year. The condition is caused by the presence of an extra chromosome 21, but it is not known what causes that extra chromosome. There is a link between maternal age and the chances of the baby having Down’s syndrome, but again the reasons for this are not known. It should be noted that most babies with Down’s syndrome are born to mothers under the age of 35, as they have higher fertility rates.

Reduce the number of invasive tests
Currently, all pregnant women are offered a Down’s syndrome test. A woman’s risk is assessed, based on her age, an ultrasound scan and markers in the blood. If the woman is assessed as having a high risk of giving birth to a child with Down’s syndrome she is offered an invasive test, which involves using a needle to take a sample of placental cells or the amniotic fluid that bathes the baby. However, this procedure carries a 1-in-100 chance of resulting in a miscarriage.

The new test looks for tiny fragments of DNA from the placenta and the foetus floating in the mother’s bloodstream, and is said to be 99% accurate. However, those with a positive result will still be offered the invasive procedure to confirm it.

The trial, which is funded by the National Institute for Health Research, will analyse the benefits of this test, as well as the best way to inform mothers and train staff about the test.

Professor Lyn Chitty, from Great Ormond Street who is leading the trial, told the BBC that this could significantly reduce the number of invasive tests and increase detection.