BLOOD TESTS ZERO IN ON DOWN FETUSES

A combination of several blood tests can identify most cases of Down syndrome in fetuses, enabling many women to avoid amniocentesis and the slight risk of miscarriage the procedure involves, doctors reported Thursday.

A study of nearly 5,400 pregnant women 35 or older showed that the new blood tests identified 89 percent of the Down syndrome fetuses but missed 11 percent.The tests also inaccurately labeled 25 percent of the pregnancies as abnormal when subsequent amniocentesis showed they were not.

The study was published in the New England Journal of Medicine.

Amniocentesis is the insertion of a needle into the womb to draw out fetal cells from the amniotic fluid so that they can be tested for chromosome abnormalities.

The procedure is routinely offered to pregnant women over 35 because their babies run a higher risk of abnormalities.

Amniocentesis detects 100 percent of fetuses with Down syndrome but is expensive and carries a risk of miscarriage.

If blood tests were used nationally to decide which women should get amniocentesis, they would miss some 350 cases of Down syndrome each year, said the study's author, Dr. James E. Haddow of the Foundation for Blood Research in Scarborough, Maine.

However, by ruling out the need for amniocentesis for many women, the blood tests could prevent the miscarriage of 14,000 normal fetuses and save up to $250 million a year in medical costs, not counting the costs associated with lifelong care for the 350 Down syndrome children missed by the blood screening, the study said.

Dr. Susan P. Pauker of the Harvard Community Health Plan said that the new blood tests will stimulate rethinking of the amnio-after-35 policy.

But she said she does not favor replacing amniocentesis in all cases with blood tests.

"Patients need to understand the values and advantage of a no-risk test vs. a test that has inherent risk of miscarriage," she said.

"This will take a lot more individualized counseling."