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Early Checking for Down's Syndrome: Still a Distant Dream

Still No Substitute for Second-Trimester Testing
By
WebMD Health News

April 21, 2000 - Madonna knows that she's expecting a boy by her 13th week of pregnancy. Can't every "mid-life" mom know in the first trimester of pregnancy if her baby has Down's syndrome? Although investigators are exploring the value of several first-trimester screening techniques, you need to know that they're just exactly that: screening tests, not diagnostic tests.

A screening test determines whether you are at increased risk of carrying a fetus with chromosomal abnormalities and whether further tests are indicated. They can't be used to make a concrete diagnosis.

The newest test, nuchal translucency, measures a space between the back of the fetus' neck and the overlying skin. A measurement higher than normal may indicate that the fetus has an increased risk of Down's syndrome or other chromosomal abnormalities. At this point, the authors point out, the challenges are the lack of a standardized definition of what normal nuchal translucency results actually are, and the fact that physicians already trained in interpreting ultrasounds need additional training to interpret nuchal translucency results.

Several first-trimester screening tests used in combination may eventually give a more accurate picture of those risks, according to a review article published recently in the American Journal of Obstetrics and Gynecology. However, because such studies are ongoing, "the current standard of care ... should not be changed," the authors write.

One ongoing study will assess the value of the nuchal translucency test in combination with other first-trimester screening techniques and compare those results to second-trimester screening. This study is called the First and Second Trimester Evaluation of Risk for aneuploidy (FASTER). Until FASTER's results are in, the authors advise that women who seek first-trimester screening only do so as study participants.

For now, what are the testing options for a mid-life mom, or any other pregnant woman concerned about chromosomal abnormalities?

"This review article doesn't change anything for most women," Donnica Moore, MD, tells WebMD. "However, pregnant women who are at high risk ... should try to participate in [FASTER] because the findings may benefit these women in future pregnancies." She is the medical commentator for NBC's "Later Today" show and the president of Sapphire Women's Health Group, a consulting and medical education group in Branchburg, N.J.

For now, the two definitive tests for Down's syndrome and other chromosomal abnormalities are amniocentesis and chorionic villi sampling (CVS). Both carry a slight risk of miscarriage. Because CVS has a somewhat higher risk of miscarriage than amniocentesis, as well as a risk of malformations, fewer women request it.

Laboratory screening tests that can help a woman know her risks include plasma protein A concentration and free beta-hCG concentration. FASTER will determine the value of a combination approach and will involve both laboratory tests such as these and nuchal translucency.

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