THURSDAY, Jan. 22, 2004 (HealthDayNews) -- Doctors in the U.S. generally reserve prenatal testing for Down syndrome and other chromosomal abnormalities for mothers-to-be who are 35 or older.

That threshold, established in the 1970s, was chosen largely because it represents the approximate age at which a woman's risk of miscarriage from having amniocentesis -- a needle extraction of amniotic fluid -- is roughly equal to her chance of giving birth to a child with Down syndrome.

But a study in the Jan. 24 issue of The Lancet finds prenatal diagnostic testing is cost-effective and should be available to all women, regardless of their age or risk of bearing a Down syndrome child.

"Women should receive the information about what their risks are," says Miriam Kuppermann, an associate professor in the Department of Obstetrics, Gynecology, and Reproductive Sciences at the University of California, San Francisco, and primary investigator on the project.

Down syndrome is among the most common genetic birth defects, affecting about one in 800 to 1,000 babies, according to the March of Dimes. An extra chromosome generally causes it. The disorder is a combination of birth defects; among them, some degree of mental retardation.

Amniocentesis is generally performed sometime during the 15th to 18th week of pregnancy, according to the U.S. Centers for Disease Control and Prevention. The procedure involves the insertion of a thin needle into the mother's abdomen to extract a small amount of amniotic fluid for testing.

Chorionic villus sampling, or CVS, is performed earlier in the pregnancy, typically during weeks 10 to 12, and involves extracting a tiny sample of placental tissue.

Both procedures are believed to increase the risk of miscarriage.

The current 35-and-older standard for amniocentesis and CVS testing assumes that women are equally concerned about procedure-related miscarriage and Down syndrome.

But women don't weigh those outcomes equally, according to Kuppermann, whose previously published research examined women's preferences. Some feel it would be more burdensome to have a Down syndrome child, she says, while others are more burdened by the threat of miscarriage.

The current study, which uses data from previously published randomized trials and other studies, compares the costs and benefits of performing amniocentesis and CVS for women of all ages and risk levels against having no invasive testing.

The tests themselves are pricey, at $1,220 for CVS and $1,120 for amniocentesis.

But the value they provide is worth the cost, at less than $15,000 per "quality-adjusted life year gained," the authors conclude.

That economic yardstick measures the costs of testing, including any miscarriages or elective abortions, against outcomes -- good or bad -- associated with the procedures, such as avoiding a Down syndrome child or having a miscarriage.

According to the study, prenatal testing falls well within the range that economists consider cost-effective for medical interventions. Anything above $50,000 per quality-adjusted life year gained becomes questionable.

So should women demand these tests?

Dr. Nancy S. Green, medical director of the March of Dimes, doesn't take a stand on whether more testing should be done.

By the time most couples must decide whether to undergo an invasive test for birth defects, they already have several bits of information in hand, she explains. The maternal serum screening, a blood test administered without any age restrictions, can help predict the risk of birth defects, for example. Parents also have ultrasound results, maternal age, and other risk factors to consider.

Still, giving women the option to have diagnostic information is a good thing, Green agrees.

"Sometimes it's really hard to get, say, an amniocentesis paid for by your insurer. You have to be high risk if you're under 35," she says.

Whether this particular study is enough to convince insurers to remove that barrier and pay for testing regardless of age and risk level remains to be seen.

In an editorial accompanying the study, Stavros Petrou of the University of Oxford in England says the cost-effectiveness of testing all pregnant women should be weighed against other competing demands on health-care resources.

"A positive decision to offer prenatal testing to all pregnant women may have broader consequences, for obstetric and other health services," Petrou writes.

More information

Visit the National Library of Medicine to learn more about amniocentesis. The March of Dimes has more on chorionic villus sampling.

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