Call for More Down Syndrome Screening
Less Invasive Tests for Genetic Defect Mean All Pregnant Women Should Be Checked, Docs Say
WebMD News Archive
Jan. 4, 2007 -- With new, less-invasive ways to check for Down syndrome,
screening for the genetic birth defect should now be offered to all pregnant
women, regardless of age, says a leading obstetricians' group.
Traditionally, pregnant women 35 and older at time of delivery have been
considered at highest risk of giving birth to a baby with Down syndrome and
have been urged to get tested.
The new recommendations from the American College of Obstetricians and
Gynecologists call for prenatal screening tests for Down syndrome to be offered
to all pregnant women.
The new screening tests are far less invasive than older, albeit more
definitive, diagnostic tests, such as amniocentesis.
While screening tests can't provide a diagnosis, they do indicate who is at
increased risk and should then be checked by amniocentesis or another invasive
test, chorionic villus sampling (CVS).
Down syndrome is a common genetic birth defect that affects approximately
one in 800 children.
Babies with Down syndrome have an extra chromosome, which causes
developmental differences in the brain and body. They can include mental
retardation, a characteristic flat facial appearance, serious heart defects,
and other medical problems.
Down Syndrome Testing No Longer Based on Age
In creating the revised recommendations, which appear in the January issue
of the journal Obstetrics and Gynecology, researchers reviewed studies on ways
to screen for Down syndrome developed in the last decade. These screens combine
ultrasound examination and blood tests.
The scientists also reviewed the age cutoff of 35 for recommending Down
syndrome diagnostic testing.
Genetic defects such as Down syndrome can be diagnosed with the more
But the test involves inserting a needle to draw a fluid sample from the
amniotic sac surrounding the fetus for genetic analysis. It isn't normally done
until the second trimester and is associated with a small risk of miscarriage.
The new, noninvasive screening tests can be performed earlier, during the
first trimester of pregnancy, giving women
more information sooner.
And although the risk of having a baby with Down syndrome does increase with
the mother's age, researchers say it is a gradual increase that doesn't jump
suddenly at 35.
New Screening Options
Topping the list of recommended first trimester tests is a screening that
combines blood tests with an ultrasound exam called a "nuchal translucency
test." This exam measures the thickness at the back of the fetus' neck.
A nuchal translucency exam alone, without the blood testing, is not as
A woman determined to be at increased risk of carrying a baby with Down
syndrome based on these tests should be offered genetic counseling and the
option of either amniocentesis or CVS, which also uses a sample of fetal cells
for genetic analysis, according to ACOG.
There are pros and cons to each testing method, ACOG says, and pregnant
women should discuss the options with a doctor.