Blood tests can identify Down syndrome fetus

September 01, 1992|By Boston Globe

By combining three blood tests, doctors can sort out younger pregnant women most likely to be carrying a fetus affected by Down syndrome, according to a recent study.

These women can then be offered amniocentesis, the definitive test for the chromosome abnormality.

The finding, reported in the New England Journal of Medicine, is important because four out of five children with Down syndrome are born to mothers younger than 35. Until now, however, doctors have recommended amniocentesis, a test for detecting a Down's fetus, only to women over 35.

The reason is that amniocentesis, which involves sticking a needle into the uterus to retrieve a sample of amniotic fluid, precipitates miscarriage in 1 case out of 200. Among women under 35, the miscarriage risk from amniocentesis is higher than the average likelihood of finding a Down fetus.

Researchers at the Foundation for Blood Research in Scarborough, Maine, and Brown University in Providence, R.I., screened 25,207 women with blood tests that measure substances sometimes found in abnormal amounts if the fetus has Down syndrome -- alpha-fetoprotein, chorionic gonadotropin and estriol. On this basis, they offered amniocentesis to about 4 percent.

The two-step screening process identified 60 percent of the expected number of Down cases.

The disadvantage is that the blood tests are valid only between the 15th and 20th weeks of pregnancy, forcing decisions to abort an affected fetus late into the second trimester of pregnancy, at higher cost, risk and emotional trauma.

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