Mother's blood test may find Down syndrome

A blood test during pregnancy more accurately and safely predicts whether a baby will have Down syndrome compared to standard screening, scientists say.
Sydney Ungvary, then three, giggles as her mother, Suzanne Ungvary, sings to her during a walk to help raise awareness for Down syndrome in Cleveland in 2007. (Joshua Gunter/The Plain Dealer/Associated Press)

A blood test during pregnancy more accurately and safely predicts whether a baby will have Down syndrome compared to standard screening, scientists say.

Researchers are investigating tests to analyze a woman's blood to spot DNA difference between her and the fetus.

Down syndrome, which results in cognitive delays, is caused by having an extra copy of chromosome 21.

Screening tests currently offered to all Canadian women involve a blood test or two and possibly an ultrasound, with an accuracy of about 80 per cent. There is no risk of miscarriage with these screening tests.

Later in pregnancy, there are prenatal tests that involve inserting a needle into the uterus to take a sample of amniotic fluid, an amniocentesis, or placental tissue for chorionic villus sampling or CVS.

These invasive tests are more accurate but involve a risk of miscarriage ranging from 0.01 per cent to 0.5 per cent for amniocentesis to one per cent for CVS, according to a 2007 guide posted on Mount Sinai Hospital's website.

Now scientists in Cyprus, Greece and England say that in a blind test, they correctly identified which fetuses were at risk of Down in 14 cases, according to the small study published in Monday's issue of the journal Nature Medicine. They also correctly screened 26 normal fetuses.

"We believe we can modify this test and make it much easier and simple," Philippos Patsalis, medical director of the Cyprus Institute of Neurology and Genetics in Nicosia, told Reuters.

It's hoped that the test could be introduced into clinical practice within two years, the researchers said.

Patsalis's method directly detected Down, also called trisomy 21, by taking a small amount of blood from the woman between the 11th and 13th week of her pregnancy.

Test measures DNA patterns

The test works by measuring differences in the DNA patterns between the woman and fetus.

"Such a non-invasive approach will avoid the risk of miscarriages of normal pregnancies caused by current, more invasive procedures," the study's authors wrote.

They are planning a larger study of about 1,000 pregnancies to check the usefulness of the approach.

Down syndrome occurs in one out of 700 live births worldwide, the researchers noted. About 500 babies are born with Down syndrome each year in Canada, according to the Canadian Down Syndrome Society. 

It's estimated the risk for a 40-year-old mother is 16  times that for a 25-year-old.

Several other research teams have published studies suggesting that analyzing the mother's blood can detect Down syndrome. 

No commercial test is available yet, but at least one company hopes to introduce one in the U.S. within about a year.

With files from The Associated Press, Australian Broadcasting Corp.