Some Older Moms-to-Be May Skip Risky Test

摘要：30, 2000 -- For nearly 25 years, doctors have routinely recommended that pregnant women age 35 and older undergo amniocentesis, a test used to detect Down‘s syndrome and other serious genetic disorders that are more common among babies born to older moms。 But new research suggests that many cou......

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Nov. 30, 2000 -- For nearly 25 years, doctors have routinely recommended that pregnant women age 35 and older undergo amniocentesis, a test used to detect Down's syndrome and other serious genetic disorders that are more common among babies born to older moms. But new research suggests that many could forgo having an "amnio" if a simple blood test performed first shows that the developing baby is likely to be normal.

Amniocentesis, in which fluid is withdrawn from the uterus and cells in it analyzed for abnormalities, is the most accurate method for determining the health of a fetus.

In 1978, a government panel recommended that all expectant moms over age 35 be offered an amnio because their risk of having a Down's syndrome baby was, at the time, felt to be higher. Up to 80% of these women currently choose to have one.

Women who undergo an amnio may miscarry, although this is rare. Many more moms suffer through the gut-wrenching, two-week wait for results. Expectant women younger than age 35, in contrast, are frequently offered a different procedure that involves drawing blood from their arm and testing it for the presence of three elements that, in abnormal levels, suggest that the fetus could have Down's syndrome. Results of the triple test, as it is called, are available in about a week.

After analyzing CDC statistics from 1974 to 1997 concerning births and mothers' ages, James Egan, MD, and his colleagues at the University of Connecticut concluded that a mother's age alone is not an accurate method for deciding who should have an amnio.

Using 1997 statistics, they found that if all women were to receive the triple test, and amnios were performed only on women whose triple tests were abnormal, 150,000 fewer amnios might have been done nationwide. Also, 1,500 more babies with Down's syndrome might have been detected, and 770 fewer fetal deaths might have occurred as a result of an amnio. The research is published in the December issue of the journal Obsterics and Gynecology.

"Age is clearly a risk factor for Down's syndrome," Egan tells WebMD. "It's just that we have a better test than we used to have, and the woman could have a blood test at 15 or 16 weeks, and 16 or 17 weeks have an amnio after getting more complete information about her risk" of carrying a child with the disease.

"There really isn't a pressing need to reduce amnios," says James Haddow, MD, one of the founders of the Foundation for Blood Research in Scarborough, Maine. Haddow and others conducted similar research in 1994. "The amnio is still the best, most reliable way to get an answer. But it would certainly be a benefit to reduce them in terms of avoiding pregnancy loss and costs. What we would like to do is find ways to reduce amnios but not sacrifice detection [of Down's syndrome]," which Haddow says is achieved with the approach of doing the triple test first.

"For women who are pregnant now, or will be in the next couple of months, this might be fresh in their minds and they might decide to go this route rather than go straight to an amnio," Haddow says.

But this idea is not without controversy. Craig Dickman, MD, an obstetrician-gynecologist in suburban Washington, D.C., says he wouldn't suggest the blood test be done before an amnio to his older moms until more studies are completed. "To say that that the triple test should replace an amnio -- I am not sure I would agree with that. It has too high a false-positive rate. I think most women want [whichever test] is the least risky and that would be blood test. But is it accurate enough?"

Stephen T. Chasen, MD, describes the issue of when to perform an amnio vs. the triple test as one charged with emotion, with fearful parents on the one side and a cost-conscious health care system on the other. Chasen agrees with Haddow that the study does a good job of rehashing this debate, but he says it won't end here.

"It is perfectly reasonable for women 35 and over to have a triple test prior to deciding to undergo amniocentesis" unless they want more assurance that the amnio can provide, says Chasen, an assistant professor of obstetrics-gynecology at Weill Medical College of Cornell University in New York. He was not involved in this study.

"A good argument can be made that too many amniocenteses are performed to identify fetuses with Down's syndrome," he says, but this is an incomplete argument. Sure, more Down's babies would be identified using the triple test and age as a guide. However, many more candidates for amnios would be found as well. More amnios mean more chances of fetal loss. "Is it worth it? Should we be asking that question of individual women?" Chasen asks.

Chasen says that up to one-fourth of the amnios he performs are on women younger than 35. At Cornell, all pregnant women, regardless of their age, are offered the triple test and amnios.

Since almost all fetuses with Down's syndrome or other abnormalities will be diagnosed, "they can then make an informed decision about whether the benefits of the test ... justify the risk [of] miscarriage," Chasen says. Women who want to be as certain as possible that they will not have a child with Down's syndrome "don't really care about the number of extra miscarriages that will be seen annually nationwide with a more liberal policy of amniocentesis. Having a child with Down's syndrome is a devastating, permanently life-altering event. Many women can accept a small individual risk of miscarriage to know that this won't happen to them."

发布日期：2006-6-27

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