New non-invasive test for Down's Syndrome for high-risk women

UK National Screening Committee recommends new non-invasive test for Down’s Syndrome for high-risk women.

Down’s Syndrome is a genetic disorder, which is caused by the presence of an additional chromosome. Most people have 23 pairs of chromosomes in each cell; however a person with Down’s syndrome will have an extra copy of chromosome 21. Down’s Syndrome often results in growth delays, impaired intellectual disability (usually of mild to moderate range) and distinct facial features.

At the moment, all pregnant women are offered combined testing for Down’s Syndrome under the NHS. This is part of the NHS Fetal Anomaly Screening Programme (FASP). The combined test consists of a blood test and a Nuchal Translucency (NT) ultrasound scan. It is undertaken during the first trimester of pregnancy, usually at 12 weeks at the same time as the dating scan. The combined test will provide a risk score for Down's Syndrome and those women who are found to be a high risk (more than 1 in 150 chance of having a baby with the condition) are offered further testing in the form of an amniocentesis test to confirm if their baby has Down's Syndrome or some other serious health condition such as spina bifida or sickle cell anaemia. Amniocentesis testing requires a sample of amniotic fluid to be taken which will then be examined and tested for Down's Syndrome amongst other serious health conditions as above. The amniotic fluid is taken by needle and is able to be tested because it contains cells from the foetus.

The test is not without its risks however as there is a 1 in a 100 risk of miscarriage and a 1 in a 1000 risk of a serious bacterial infection.  

The new screening method being recommended by the UK National Screening Committee (NSC) is Non Invasive Prenatal Testing (NIPT), also known as Cell free fetal DNA (cffDNA), which as per its name is non-invasive and therefore carries no risk of miscarriage. Not only does it carry no risks but it is thought to be much more accurate than the combined test, with around 99% accuracy.

NIPT involves taking a sample of the mother’s blood from the arm like a normal blood test, which is then sent off for testing. There is fetal DNA in the mother’s blood which enables the foetuses’ genetic profile to be tested for Down’s Syndrome amongst other conditions. The NIPT cannot be undertaken before week 10 of pregnancy, because there is not enough fetal DNA in the blood to allow for testing. Once undertaken, the results should be available within 7 to 10 working days.

At present NIPT is not available on the NHS (although it is offered to many women attending private clinics across the country); however the UK NSC who have carried out research into the appropriateness of offering NIPT across the NHS, have published a recommendation that NIPT be introduced as an additional test into the NHS FASP programme to those women who are found to be high-risk. By doing so, less women will have to have the invasive amniocentesis testing; hopefully resulting in less miscarriages as a result. It is now up to the ministers for the Department of Health to approve the UK NSC’s recommendations and it is hoped that this will take place shortly.

Key facts about Down’s syndrome: Did you know…?

• Around one in every 1000 babies born in the UK will have Down’s syndrome.
• There are over 40,000 people in the UK with the condition.
• Although the chance of a baby having Down’s syndrome is higher for older mothers, more babies with Down’s syndrome are born to younger women.
• Down’s syndrome is not a disease. People with Down’s syndrome are not ill and do not “suffer” from the condition.
• Today the average life expectancy for a person with Down’s syndrome is between 50 and 60 with a small number of people living into their 70s and beyond.¹

^1. Down's Syndrome Association