New blood test for Down's that lowers risk of miscarriage: Screening more accurate and safer for babies
06:48 GMT, 4 September 2012
Ultrasound: Currently women are offered a screening towards the end of their first trimester
Doctors have developed a blood test for pregnant women that can detect 99 per cent of Down’s syndrome babies without risking a miscarriage.
The test is used in the 12th week of pregnancy and could save hundreds of healthy babies being lost each year.
It examines DNA in cells from the unborn baby found in the mother’s blood and looks for evidence of chromosomal abnormalities that cause Down’s and similar genetic disorders.
A study by the foetal medicine specialist Professor Kypros Nicolaides in London shows the Harmony prenatal test is highly accurate at a very early stage in pregnancy.
It is one of several in development promising a new era in prenatal screening that will be available not only to those at high risk of having a Down’s baby, but routinely used to reassure all pregnant women.
Currently they are offered a nuchal fold test, which uses ultrasound screening to measure fluid at the back of the baby’s neck at 11 weeks.
Those deemed to be at high risk are offered amniocentesis or chorionic villus sampling, in which a needle is inserted into the womb to remove amniotic fluid or a piece of placenta for genetic testing.
This can endanger the baby and is offered only to high-risk women as it can cause miscarriage in between one in 100 and one in 200 cases.
Unsafe procedure: The ultrasound screening is considered a high risk and the new test is said to be a safer alternative
Some of these babies would have been born healthy – around 300 a year are lost – so many prospective parents decline testing.
The latest study involved 2,049 women in the 12th week of pregnancy and detected all cases of Down’s syndrome.
There was a false-positive rate of just 0.1 per cent, meaning one pregnant woman in 1,000 was offered an unnecessary invasive test.
The false-positive rate of traditional screening after nuchal fold measurement is 4.5 per cent.
The study by Prof Nicolaides and his team at the Harris Birthright Research Centre for Foetal Medicine at King’s College Hospital in London was supported by the Foetal Medicine Foundation, a UK charity.
The findings were published in the American Journal of Obstetrics and Gynecology.
The blood test analyses DNA cells from the baby found in the mother's blood
Prof Nicolaides, who developed the nuchal fold test, said: ‘I have been leading research in this area for the past 20 years, and this new study gives us a very positive development.
‘It means we can detect more than 99 per cent of affected pregnancies, rather than 90 per cent with the currently used methods.
‘Additionally, only one in 1,000 pregnant women will have to undergo an unnecessary invasive procedure, which is a dramatic reduction from the 50 in 1,000 women undergoing this procedure in the past.
‘What’s even more exciting is that this test is highly accurate for routine screening of all pregnant women, not just those deemed high risk.’
The cost of the test, which was made available last month at a chain of US clinics for $700 (440), has yet to be decided for UK patients but is likely to be less than 1,000.
At least one other non-invasive test is being evaluated by NHS laboratories while two others are in clinical trials. Widespread use of any such test on the NHS would have to be approved by the National Screening Committee and the cost would be a decisive factor.
But evidence from trials such as the latest study will prove compelling, as it shows the risk of miscarriage is removed for most women opting for screening.
About 1,100 cases of Down’s syndrome are diagnosed in pregnancy each year and about 90 per cent of them lead to abortions.
However, with many parents declining screening or a termination, about 750 babies with Down’s are born annually.
Ken Song of Ariosa Diagnostics, the US firm that developed the Harmony test, said: ‘We have now studied over 6,000 women, including 2,000 low-risk women, across multiple studies.
‘The Harmony prenatal test represents a major advance in obstetrics that can provide highly accurate information to women so as to better manage their pregnancy.’