Amiga Plus 1995 #2/Amiga Plus CD - 1995 - No. 2.iso/internet/faq/englisch/misc.kids-ultrasound

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Archive-name: misc-kids/pregnancy/screening/ultrasound
Posting-Frequency: monthly
Last-Modified: February 16, 1995

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          Misc.kids Frequently Asked Questions
                Ultrasound

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Collection maintained by: Lynn Gazis-Sax ([e-mail])

To contribute to this collection, please send e-mail to the address
given above, and ask me to add your comments to the FAQ file on
AFP Screen and the Triple Screen.  Please try to be as concise as possible,
as these FAQ files tend to be quite long as it is.  And, unless
otherwise requested, your name and e-mail address will remain in the
file, so that interested readers may follow-up directly for more
information/discussion.

For a list of other FAQ topics, ftp to the pub/usenet/misc-kids directory
  of rtfm.mit.edu or tune in to misc.kids.info.
=====
Copyright 1995, Lynn Gazis-Sax.  Use and copying of this information are
permitted as long as (1) no fees or compensation are charged for
use, copies or access to this information, and (2) this copyright
notice is included intact.
====
=====================================================================
[NOTE: this is information collected from many sources and while I
have strived to be accurate and complete, I cannot guarantee that I
have succeeded.  This is not medical advice.  For that, see your
doctor or other health care provider.]
=====================================================================
Acknowledgements:
Many people helped with the prenatal testing FAQs by advising about
the best way to structure them, by contributing stories and information,
or by reviewing versions of the FAQs.  A list of acknowledgements can
be found in the Prenatal Tests: Overview FAQ.
=====================================================================
Note on language: When I first posted the questions for the prenatal testing
FAQs, I used the term "birth defects" (except for question 7 of the Prenatal
Testing Overview FAQ).  Since I have been advised that this term may be
offensive to people in the disabled community, I changed the wording of the
final FAQs to use the word "disability," but most replies still reflect the
original wording of the questions.
=====================================================================


IV. Ultrasound

1. What are the different kinds of ultrasound and what can they detect?

Ultrasound is high frequency sound waves which are used to visualize the
fetus in utero.  It works in a fashion similar to sonar.  There are three
kinds of ultrasound.  Level One ultrasound produces a one or two
dimensional picture and is used for detecting "fetal age, size, weight,
presentation, placental location, and appearance of major fetal body
parts" (Blatt).  Real time, or Level Two ultrasound is a series of still
pictures in rapid succession to show motion.  It is used for prenatal
diagnosis or together with amniocentesis, chorionic villus sampling, or
fetal blood sampling.  Doppler ultrasound is a continuous rather than
intermittent wave beam.  It is used to evaluate the fetal heart rate, and
is used in overdue women to check for fetal distress.  Another way of
distinguishing different kinds of ultrasound is by the kind of probe used
- vaginal or abdominal (see answer below to question about full bladder).

Ultrasound is used at a variety of different points in pregnancy to detect
a variety of different things.  Uses of ultrasound include: 1) to guide
instruments for prenatal diagnosis (as, for example, the needle used in
amniocentesis), 2) to confirm pregnancy, 3) to locate the baby (useful in
ruling out ectopic pregnancy), 4) pregnancy dating, 5) to determine
whether there is more than one baby, 6) to check the baby's growth, 7) to
evaluate movement, tone, and breathing, 8) to identify sex (not as
reliably as amniocentesis - don't paint the nursery based on this
information), 9) to asses the amount of amniotic fluid, 10) as an adjunct
to cervical cerclage or suture, 11) to look for molar pregnancies, 12) to
determine the structure and position of the placenta (particularly useful
if placenta previa is suspected), 13) to determine the cause of bleeding,
14) for fetal surgery, and 15) to confirm fetal death.  Details on all of
these uses can be found in _Prenatal Tests_ by Robin Blatt. Some places
(e.g. India) are considering outlawing informing the parents of the sex of
the child based on ultrasound, because of the tendency for female children
to be aborted.

The disabilities which ultrasound can detect are structural defects
which show up in the picture of the fetus, for example, anencephaly (by
the twelfth week of pregnancy), spina bifida (by the twentieth week),
disorders of the skeleton, central nervous system, heart, kidneys, or urinary
tract.   Ultrasound does *not* detect the severity of spina bifida, only
whether it is present.

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From [e-mail] (Robert Brenner MD):

Ultrasound can detect numerous structural defects.  The list is too long
to mention.  ULTRASOUND CANNOT DETECT DOWN SYNDROME WITH ANY DEGREE OF
ACCURACY.  The American College of OBGYN states that routine ultrasound is
not cost effective and does not influence neonatal outcome.  Therefore,
ultrasound is recommended only for indicated reasons such as bleeding,
inaccurate dates, large or small for dates, family history or past history
of structural birth defects that can be diagnosed by ultrasound, elevated
AFP, abnormal triple screen, and for guidance at the time of
amniocentesis.  Late in pregnancy ultrasound is used to determine fetal
well being, the amount of amniotic fluid, the position of the fetus, and
to get an estimate of the size of the fetus.  Ultrasound is routinely used
to follow fetal growth in multiple gestations as well as fetuses who are
small for gestational age.
-----------------------------------------


2. What can ultrasound not detect?

It can't detect disabilities which aren't visible structurally.  It
would not, for example, detect sickle cell anemia.  It might detect Down
syndrome in some cases, if some of the characteristic Down syndrome
features were visible, but it might well not.

-----------------------------------------
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.
-----------------------------------------

(The nuchal fold is on the back of the neck.)

3. How accurate is ultrasound, and what are possible sources of error?

The accuracy of ultrasound for dating a pregnancy depends on at what point
during the pregnancy the ultrasound is taken.  Pregnancy dating is most
accurate during the first half of pregnancy.  Measurement of the sac at
five to seven weeks gives an accuracy of plus or minus ten days.
Measuring the crown-rump length gives an accuracy of plus or minus three
days at seven weeks; this test can be used from the seventh to the
fourteenth week.  Between fourteen and twenty-six weeks, the measurement
of the biparietal diameter of the baby's head, the femur length, and the
head and abdominal circumference is used; the accuracy is plus or minus
seven to ten days.  Later in pregnancy, the accuracy declines, and may be
plus or minus twenty-one days.

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From Dr. T. Reynolds:

The reason for this is that different babies grow at different rates and that
all measurements are subject to inacccuracy because the object being measured
is not linear (e.g. a babies head is not a sphere, it is an ellipsoid, so
it is possible to get different slightly measurements depending on what
position the baby lies in.
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I haven't found many estimates of exactly how accurate ultrasound is at
detecting disabilities, but there are both false negatives and false
positives.  The accuracy will vary depending on the experience of the
person doing the ultrasound.  The accuracy also varies with which
condition is being detected. For Down Syndrome, it is very low.  For
anencephaly, on the other hand, it is highly effective.

Some estimates:

"The use of routine ultrasound, including a four-chamber view of the
heart, can lead to the diagnosis of approximately 50 percent of major
cardiac, kidney, and bladder abnormalities that would not be detected by
maternal serum alpha-fetoprotein screening. When targetted ultrasound
examination is performed by skilled ultrasonographers to detect
malformations suspected on the basis of the history or the screening
ultrasonogram, the sensitivity and specificity of this procedure are
greater than 90 percent." (NEJM, 1/14/93, Prenatal Diagnosis) It is
estimated that ultrasound can detect 81% of ectopic pregnancies (Brit
Journal of Obst and Gyn, Dec 1988, Vol 95, pp 1253-1256). Ultrasound is
most effective for gross structural abnormalities.  It is highly effective
for anencephaly. (Medical Intelligence. Chervenak et al. Advances in the
Diagnosis of fetal defects.)


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From Dr. T. Reynolds

For spina bifida there is definitely evidence (but I can't remember where I saw
it) that diagnostic accuracy is improved by having the AFP test: i.e. a high
AFP result concentrates the mind of the ultrasonographer and they look for and
often spot smaller neural tube defects. It is for this reason that some centres
continued screening for spina bifida using AFP even when ultrasound arrived and
certain quarters called for an end to the blood test because it was unnecessary
duplication.
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4. What are the risks of ultrasound?

This question turns out to be controversial.  Some of the books which I
consulted reassured that ultrasound has been used for decades with little
risk, and that, while more studies could be done, the studies which have
been done confirm its safety.  "Although the effects of ultrasound are
still being studied, no harmful effects to either the mother or the baby
have been found in over 20 years of use.  The long-term risks of
ultrasound, if any, are unknown, but there are many benefits." (ACOG)

Others warn that it is insufficiently tested, and make comparisons with
X-rays and DES, which were once considered safe.  The main area of debate
is whether ultrasound is being used too frequently in a routine fashion in
healthy pregnancies, without thorough enough testing.  There may be some
association between ultrasound and low birth weight (Blatt).  (Altho' this
is difficult to prove because the opposite assertion is known to be true:
i.e. if there is IUGR (intra-uterine growth retardation) US will be
performed more regularly to assess the progress of the baby.)
Some people express concern about the heat and cavitation (bubbling in
the cells).  Others wonder whether routine ultrasound is cost effective,
or whether the money involved would be more effectively spent elsewhere.

A Consensus Development Conference of the National Institutes of Health
(NIH) was convened to consider the use of ultrasound in pregnancy, and
concluded that "Diagnostic ultrasound is considered to be a low-risk
procedure.  However, routine use of ultrasound in pregnancy should be
discouraged."  (Blatt) They recommended ultrasound only for twenty-eight
specific instances.  (The use of diagnostic ultrasound in pregnancy.
Washington, DC.  Government Printing Office, 1984.) In contrast, Germany,
France, and the UK have adopted a policy of ultrasound for all
pregnancies. (NEJM, 1/14/93, Prenatal Diagnosis)

-----------------------------------------
From [e-mail] (Robert Brenner MD):

The theoretical risk of fetal exposure to sound waves has never been shown
to cause any fetal damage.  The biggest risk of ultrasound is
overinterpretation or missed diagnosis.
-----------------------------------------


5. Do you really have to have a full bladder for an ultrasound?

Women getting an ultrasound are encouraged to drink several glasses of
water an hour before the exam and not go to the bathroom until after the
exam.  The full bladder helps the doctor locate the pelvic organs and get
a clearer and more accurate picture.  However, this advice only applies
for some ultrasounds, depending on the kind of probe used and the point
in pregnancy when the ultrasound is done.  This is why different women
report getting different advice from their doctors about whether a full
bladder is required.

-----------------------------------------
From [e-mail] (Robert Brenner MD):

The two types of ultrasound are abdominal and vaginal ultrasound.  Vaginal
ultrasound is the most accurate up to 12 weeks gestation and does not
require a full bladder.  Abdominal ultrasound requires a full bladder up
to about 14-16 weeks.
-----------------------------------------

Sources:

The American College of Obstetricians and Gynecologists (abbreviated in
references as ACOG).  Planning for Pregnancy, Birth, and Beyond.  A
Dutton Book, May, 1992.

Blatt, Robin J.R.  Prenatal Tests. Vintage Books.  New York, August 1988.

The Boston Women's Health Collective.  The New Our Bodies, Our Selves.
Simon and Schuster.  New York, NY, 1992.

Rothman, Barbara Katz.  The Tentative Pregnancy. Viking Penguin Inc.  New
York, NY, 1986.

Scher, Jonathan, M.D., and Dix, Carol. Will My Baby Be Normal?  How to
Make Sure.  The Dial Press. New York. 1983.

Lynn Gazis-Sax