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2. What can ultrasound not detect?




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This article is from the Pregnancy Screening FAQ, by Lynn Gazis-Sax (gazissax@netcom.com) with numerous contributions by others.

2. What can ultrasound not detect?

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From Franklin Tessler, MD, CM (FTessler@aol.com)

As far as detecting fetal abnormalities goes, several points need to
be made:

a) Not every problem can be diagnosed with ultrasound -- conditions
which do not manifest as a structural or gross functional abnormality
(such as a very abnormal heart beat) may be missed.

b) Not every problem which can be detected will be diagnosed. For
example, the basic ultrasound exam (for which there are published
guidelines) does not include counting the baby's fingers and toes,
even though it is possible to do so should it be necessary.

c) The sensitivity of an ultrasound exam depends on a number of
factors, such as the size and position of the fetus, the body habitus
of the mother, the type of equipment used, and, most importantly, the
skill and experience of the operator. Concerned parents-to-be may want
to inquire politely about the training and experience of the person
performing or interpreting their sonogram.

d) Some problems (such as anencephaly) are more readily diagnosed than
others (such as cleft palate).

In the third trimester, ultrasound can be used to detect problems that
may affect planning of delivery, such as intrauterine growth
retardation (IUGR). As mentioned elsewhere, dating during this stage
of pregnancy tends to be less accurate because biological variability
is greater.

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From Dr. T. Reynolds:

Amazing claims are being made about nuchal fold thickness measurement as
a screening technique for Down's but this technique is being performed in
highly specialised teaching centres and there is as yet no evidence that the
test could be carried out in 'lower-tech' local hospitals.
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(The nuchal fold is on the back of the neck.)

 

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