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Home > Research Articles > New method to screen for Down's syndrome

San Jose Mercury News

Wednesday, October 22, 2003

San Jose Mercury News - October 09, 2003

A new combination of tests may detect Down's syndrome in fetuses earlier and more accurately than current screening methods, according to a new study.

But some experts viewed the study's findings cautiously, saying widespread debate remains over the best way to screen pregnant women for the fetal genetic disorder, which causes mental retardation and other health problems in babies.

Researchers conducting the study, published today in the New England Journal of Medicine, found that combining blood tests with specialized ultrasound exams caught about 85 percent of Down's syndrome cases in the first trimester of pregnancy, although there was a "false positive" rate of nearly 10 percent. A false positive result erroneously shows a healthy fetus to have Down's syndrome.

The study of more than 8,200 women was led by a researcher from Philadelphia-based Drexel University College of Medicine.

Down's syndrome, caused by an extra copy of a chromosome, occurs in one in every 800 to 1,000 live births. Today, Down's syndrome affects more than 350,000 people in the United States. Affected children have mild to moderate mental retardation, with many displaying such characteristics as a flat face.

Pregnant women in the United States now typically receive blood tests for "markers," often proteins or hormones associated with a higher risk of Down's syndrome. But those tests are performed in the second trimester, when it is riskier for the mother to terminate a pregnancy, and currently have a success rate of about 65 percent, according to the researchers.

If the blood tests show a higher risk, more invasive tests are then offered for a more definitive diagnosis. These tests, such as amniocentesis and chorionic villus sampling are more certain than blood tests or ultrasound exams, but can cause miscarriages. They are generally offered only to women over 35, who face a one in 270 chance of carrying a Down's syndrome baby.

In the New England Journal of Medicine study, researchers performed ultrasound tests for an enlarged, fluid-filled area at the back of the baby's neck that can signal Down's syndrome. They also tested women for a particular protein and hormone that may also signal the presence of the disorder, and used maternal age in estimating a woman's risk.

Supporters of first-trimester, non-invasive screening for Down's syndrome say it offers women the option to either terminate their pregnancies more safely and easily before they are visibly pregnant -- or plan ahead for their child should they choose to carry to term.

Still, most physicians and researchers are waiting for the results of a larger and more definitive study examining the effectiveness of numerous Down's syndrome screening methods before changing their recommendations for pregnant women, said Dr. James Goldberg, co-director of the Prenatal Diagnosis Center at the California Pacific Medical Center in San Francisco. The results of that study are expected in February.

The New England Journal of Medicine also published a more cautious view. An editorial published alongside the study warned that later screening should remain standard practice until more research is completed and detailed guidelines can be established to guide doctors and pregnant women.

Dr. Rebecca Smith-Bindman, a University of California-San Francisco researcher, who has studied Down's syndrome screening, said the combination of tests looked "promising" but cautioned that the ultrasound screening in the study is difficult to perform accurately.

Callie Grant, a Menlo Park educational writer who is 8 1/2 months pregnant, said she and her husband would not have terminated her pregnancy, precious at her age of 41, even if their baby had Down's syndrome.

"When you see your baby on an ultrasound, you really form a bond with it," Grant said. "Even if doctors can predict Down's syndrome earlier, it doesn't make decisions any easier."

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