New blood test for Down's that lowers risk of miscarriage: Screening more accurate and safer
for babies
4 September 2012
dailymail.co.uk
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.’
3 September 2012
rd
Pregnancy blood test can identify Down's syndrome
newscientist.com
TESTING whether a fetus has Down's syndrome is getting easier - and less risky. Several companies, all based
in California, are launching tests that work on a pregnant woman's blood, rather than requiring an invasive
procedure. The tests are already proving controversial, with opponents of abortion concerned that more women
will decide to terminate their pregnancy. "We oppose testing for the purpose of killing unborn children who are
found to have disabilities," says Jessica Rodgers, spokeswoman for the National Right to Life Committee. Brian
Skotko, a Down's syndrome researcher at Boston Children's Hospital, says this isn't an unreasonable concern.
The new tests will see prenatal diagnoses skyrocket, he says. "Unless the healthcare community ensures that
these women receive accurate information about Down's syndrome, I think that a reasonable prediction is that
fewer babies with the syndrome will be born." Down's syndrome, caused by an extra copy of chromosome 21, is
generally detected by amniocentesis, which involves inserting a needle into a pregnant woman's belly to sample
cells from the fluid bathing her fetus. It carries a 1 per cent risk of miscarriage and is usually performed
between 15 and 20 weeks into pregnancy - which in some US states is right up against the legal time limit for
abortion. Chorionic villus sampling, which samples tissue from the placenta, can be performed earlier, but has
an even higher risk. The new tests instead detect DNA from fetal cells that have broken down. Some of this
DNA crosses the placenta and gets into the mother's bloodstream, and the tests look for an excess of material
from fetal chromosome 21. First out of the gate was Sequenom of San Diego, which launched its long-awaited
test for Down's last October. Verinata of Redwood City released its test in March, while Ariosa Diagnostics of
San Jose will launch a test this week; both of these can detect extra copies of chromosomes 13 and 18 too,
each associated with distinct chromosomal conditions. Later this year, Natera of San Carlos will market a test
that can also detect additional copies of the X and Y sex chromosomes. Not only do the blood tests eliminate
the risk of miscarriage, they are also claimed to have lower error rates than conventional tests. At a conference
on prenatal genetic testing at Stanford University in California last week, Kenneth Song of Ariosa said that its
test turns up false positives in less than 0.1 per cent of cases - compared with 5 per cent from invasive tests.
The other companies report similar results. The new tests can be run from about 10 weeks into pregnancy. In
some US states, the extra time this will allow may be crucial as women decide whether to carry a fetus to term.
Nine states currently ban abortions after 20 weeks on the grounds that a fetus can feel pain at this age; 11
others are considering such legislation. Will the extra time lead to a surge in abortions? That fear "gives women
too little credit", argues Jaime King of the University of California Hastings College of the Law in San Francisco.
She suggests that if women have more time to gather information on raising disabled children they might be
more likely to keep the pregnancy.