Ultrasound Findings May Not Predict Down Syndrome
Reuters, The Journal of the American Medical Association 2001;285:1044

New York, NY -- Second-trimester ultrasound is a poor method of detecting
Down syndrome in unborn children, researchers report, and may lead to
erroneous abortion decisions, or a false sense of security for those who
get a negative result.

Only one specific ultrasound marker -- a thickening of the skin at the
back of the unborn child's neck known as the nuchal fold -- seems to be a
predictor of Down syndrome. But even this marker may not pick up enough
cases to make ultrasound a practical screening method. Not all unborn
children with Down syndrome have a nuchal fold thickening.

Other methods checked by ultrasound--such as shortened bones in the leg or
arm, a brain cyst or white spots seen in the bowel--were ``not helpful in
confirming or excluding the presence of Down syndrome,'' conclude Dr.
Rebecca Smith-Bindman, of the University of California, San Francisco, and
associates.

The researchers reviewed the results of 56 studies on second-trimester
ultrasound, involving over 130,000 unborn children. The researchers looked
at so-called markers, or ``soft signs'' of Down syndrome, which are
ultrasound findings that in and of themselves are not abnormalities.
These, combined with blood tests and clear structural abnormalities--such
as heart problems--are used to predict Down syndrome.

The findings are reported in the February 28th issue of The Journal of the
American Medical Association.

The ability of ultrasound markers to accurately detect Down syndrome on
their own was relatively low, the authors report, meaning that the test
might miss a large number of cases. The researchers note that even using
the best measure--nuchal thickening--meant that between 4,454 high-risk
women or 87,413 average-risk women would need to be screened to detect
just one case of Down syndrome.

On the other hand, testing for ultrasound markers could also lead to
false-positives--results that incorrectly suggest that a healthy unborn
child has Down syndrome. This may cause woman to opt for more conclusive,
invasive tests, such as amniocentesis.

During amniocentesis a needle is used to extract a small amount of
amniotic fluid from the womb, a procedure that carries a small risk of
miscarriage. The researchers estimate that for every one case of Down
syndrome picked up by the measurements, 79 (for nuchal fold) to more than
600 women would get a false-positive diagnosis.

``The use of the ultrasonographic markers as an indicator for invasive
testing with amniocentesis will lead to an increase in the number of
unaffected fetuses lost as a complication of the procedure,''
Smith-Bindman's team writes.

``Most physicians who I speak with don't really like using
(second-trimester ultrasound),'' she told Reuters Health. ``They don't
believe they are helpful in identifying babies truly affected by Down
syndrome. But in this medical-legal environment, they feel that once
they've seen it, they're compelled to explain it to the woman and
therefore recommend invasive testing.''

This causes a huge amount of anxiety for women, Smith-Bindman noted.
``Unfortunately, even when a second ultrasound or amniocentesis shows the
baby is normal, women remain stressed about it until the end of
pregnancy,'' she said. ''Women are concerned if they've been told, for
example, that their baby had a cyst in the brain.''

However, the study results are not the final word on ultrasound screening,
according to Dr. Charles Lockwood, the professor and chairman of the
department of obstetrics and gynecology at New York University. The
analysis lumps together many studies from many different centers, which
can often have widely varying ultrasound results depending on the
equipment and skill of the people performing the tests.

According to Lockwood, the ``curse'' of reviewing dozens of different
studies ``is that you can never truly compare studies from center to
center.'' He also notes that the study did not even look at ultrasound
screening in the first trimester. Lockwood and colleagues are conducting a
trial, known as FASTER, in which ultrasound screening for nuchal fold
thickening is performed in the first trimester, and used in combination
with a blood test to try to predict Down syndrome risk.

``I think there is a role for ultrasound in better defining risk,'' he
said. ``I don't think it's a great approach, I have a funny feeling that
the FASTER trial is going to show that first trimester is the way to go
but I don't know that for a fact.''

He believes that if women opt for ultrasound screening, they should only
go to centers that specialize in the techniques, and that use the latest
and most sophisticated equipment. ``It's not something doctors should be
doing in their office,'' he said. ``If you don't have that kind of
experience and expertise, and vast numbers of publications coming out of
your center on this topic, you shouldn't be doing it,'' said Lockwood.