Should Age Determine Prenatal Testing?

Study Challenges Long-Held Practice of Reserving Tests Mostly for Women 35 and Older

From the WebMD Archives

Jan. 22, 2004 -- A new study challenges the popular notion that only pregnant women age 35 and older should get prenatal testing.

Study researchers say that age shouldn't be the primary criteria in whether or not to be tested. No matter the woman's age, prenatal diagnostic testing is cost-effective under these criteria, they explain in this week's issue of The Lancet.

Since prenatal testing guidelines were first developed in the 1970s, age has largely dictated which expectant mothers get fetal screening tests that detect birth defects but also boost miscarriage risk.

No matter their overall health, most pregnant women age 35 or older are advised to get an amniocentesis or CVS test to determine whether their developing baby has Down syndrome or another chromosomal abnormality. But these tests are usually not done on younger women, unless they are deemed to be at high risk of birthing a child with Down syndrome or another problem.

The reason: Risk of these defects steadily increases with later-age pregnancy, with 35 being the long-designated age at which these invasive diagnostic tests seem to make sense. At this age the risk of procedure-related miscarriage risk is almost equal to the chance that a child will be born with Down syndrome, according to the authors. They also say that the cost of offering aminocentesis would be offset by the savings associated with preventing the birth of an infant affected by Down syndrome.

"We're not pushing for or discouraging against amniocentesis or CVS testing for pregnant women," Miriam Kuppermann, PhD, tells WebMD. "What we're saying is that women should be allowed to choose for themselves whether or not to undergo testing -- regardless of their age."

Traditionally, one of these diagnostic tests has been routinely recommended for women who are pregnant at age 35, but not for younger women. Largely, this results from the fact that before age 35, the risk of birthing a baby with Down syndrome is almost 1 in 1,000; at 35, it jumps to almost 1 in 400 and increases with each year. Additionally, there is some type of chromosomal abnormality in about half of pregnancies that end in miscarriage, reports the American College of Obstetricians and Gynecologists.


But either test -- typically costing about $1,000 -- can also slightly boost miscarriage risk, which is why they're usually not recommended for younger women unless they are deemed higher risk of birthing a baby with Down syndrome. In amniocentesis, done between 14 and 18 weeks of pregnancy, a needle is inserted into the womb and a small amount of fluid that surrounds the fetus is withdrawn for chromosomal testing. With chorionic villus sampling (CVS), which can be done several weeks earlier, a needle is passed into the womb to remove and examine a small amount of tissue in the placenta.

In this study, Kuppermann and her colleagues at the University of California, San Francisco, did a cost-utility analysis of either getting or not getting the two prenatal tests in 534 pregnant women between ages 16 and 47. This analysis measured several factors -- the cost and effectiveness of the tests against the risk of miscarriage and benefits of detecting a fetal chromosomal abnormality. The women studied preferred procedure-related miscarriage risks to having a baby with Down syndrome.

All age groups had a similar cost-effectiveness based on quality-of-life years gained from information from the test - that is, knowing before birth whether the baby had Down syndrome or another condition.

"Some interventions are life-saving and have no impact on the quality of life," Kuppermann tells WebMD. "Some might be life-saving and also impact quality of life. Some have no effect on life expectancy, but have a huge affect on the quality of life. These prenatal tests are in the latter category."

But at least one expert, who wrote an accompanying editorial to Kuppermann's study, tells WebMD that these calculations were made without making some important considerations.

"I have concerns about the failure to recognize that the unborn child diagnosed with a chromosomal abnormality has the potential to produce future benefits, while only recognizing it has the potential to incur future costs," says Stavros Petrou, PhD, health economist at the University of Oxford.

"I am also concerned about the failure to compare the cost-effectiveness of universal prenatal diagnostic testing against some of the screening programs currently available in most industrialized nations," he tells WebMD.

One alternative being investigated combines tests for certain biological markers in the blood and ultrasound measurement of what's known as nuchal translucency -- thickness of skin behind the fetus' neck. In one study presented two years ago before the Society for Maternal-Fetal Medicine, researchers reported that these measures detected with 85% accuracy whether a fetus had the chromosomal abnormality that causes Down syndrome. By comparison, certain tests, such as one that screens for high amounts of alfa fetal protein (a red flag for fetal abnormality), identify only 65% of cases and falsely ID about 5% of women, they said.

WebMD Health News


SOURCES: Harris, R, The Lancet, Jan. 24, 2004; vol 363: pp 276-282. Miriam Kuppermann, PhD, MPH, associate professor of epidemiology and biostatistics, University of California, School of Medicine, San Francisco. Stavros Petrou, PhD, health economist, National Perinatal Epidemiology unit, University of Oxford, U.K. Clinical Management Guidelines for Obstetricians-Gynecologists, the American College of Obstetricians and Gynecologists. WebMD article, "Earlier Testing for Down Syndrome," Jan. 17, 2002.
© 2004 WebMD, Inc. All rights Reserved.


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