Early Checking for Down's Syndrome: Still a Distant Dream
Still No Substitute for Second-Trimester Testing
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
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
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.