New Blood Test Means Safer Prenatal Screening

A British study has shown a new blood test to be safe and effective for detecting chromosomal problems in fetuses.  The test looks for problems in the baby’s DNA, such as when a third copy of a chromosome is present.  This condition, known as trisomy, is responsible for incurable disorders such as Down Syndrome.  The test does not only screen for trisomy 21, which causes Down Syndrome, but also trisomy 18 and trisomy 13.

While many children with trisomy 21 can survive with medical treatment, babies with trisomy 18 often die before they are born.  If they do survive they often have serious deformities of the heart and kidneys and usually do not live long.  Similarly, many fetuses with trisomy 13 die in the womb.  Of those that are born, 80% die in their first year, and most have severe deformities.

All of these chromosomal disorders are more common in children born to mothers over 35.  The disorders may also be linked to older paternal age.  As more people delay marriage and childbirth, more and more children are born to parents in this vulnerable age group. Accordingly, there is an increased demand for tests so that families can know if their babies are healthy.

Other tests that look for chromosomal problems in the fetus, such as chorionic villi sampling (CVS) and amniocentesis, take samples of tissue or amniotic fluid to look at the baby’s DNA.  While these tests are effective, they can also cause miscarriage.  For some families the odds of these tests causing a miscarriage are the same as the odds of the test detecting any health problems in their babies.  Even aside from this serious risk, the tests are invasive, can be painful for the mother, and are often very expensive.

The new blood test is free from many of these problems.  The test requires a small sample of the mother’s blood.  Very small amounts of fetal DNA circulate in the blood of pregnant women.  The test is able to amplify these small amounts of fetal DNA to look for possible health conditions in the fetus.  Because the test is not invasive and does not require a sample from the baby or the placenta, it does not increase the risk of miscarriage.

The new blood test is also more accurate than many of the old tests for chromosomal problems.  It delivers false positives only 0.1% of the time.  This means that the test will say there is a problem when really the baby is healthy in much less than 1% of cases.  In the British study the blood test was found to accurately detect problems 98% of the time.The blood test can be performed at 10-12 weeks gestation.  This means the test can be done in the first trimester; earlier in the pregnancy than many other tests.  The new blood test will give families more time to make decisions about the results.  In most cases, families will be able to relax earlier in pregnancy, knowing that their babies are healthy.