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Skip the Amniocenteses?
by
George P. Henry, M.D.
Board Certified OB-GYN
Board Certified Clinical Genetics and Clinical Cytogenetics
I recently asked an
Ob/Genetics colleague if amniocenteses were vanishing in his region and
he
answered-“like the buffalo”! This should be an enormous concern to all
of us
involved in women’s health care.
The acceptance of genetic amniocentesis
should be
increasing. I believe it is falling
because women are being misinformed and misled toward accepting First
Trimester
Risk Estimation (by nuchal translucency measurement plus assay of B
subunit hCG
and Papp-A) or second trimester ultrasound as a substitute for an
indicated
genetic amniocentesis. Patients and
physicians need to understand that ultrasound and serum assays cannot
diagnose
or rule out any chromosome abnormality. They
are not diagnostic.
I applaud risk estimations (more correct than
“screening”) in the first or second trimester to identify pregnancies
which
were not previously known to be at sufficient risk to offer diagnostic
testing. More couples may then
benefit
from prenatal diagnosis. The use of the term invasive testing
for either
CVS or amniocentesis should be abandoned as a prejudicial nudge against
indicated diagnostic testing.
CVS is usually quoted as having a 1% risk of pregnancy
loss by its strongest proponents. That
is a risk pregnant women may accept or decline.
Second trimester amniocentesis has for decades been
misquoted as having a 1 in 200 risk of pregnancy loss.
It was reported at the December NIH anel
that the federally funded FASTER Trial finds the risk of loss in
multiple centers
with multiple operators to be 1 in 1100 (0.09%)[1]. This is less
than one in a thousand!
This extraordinary level of safety must, of necessity,
change all discussions with patients regarding prenatal genetic
diagnosis. It
had previously been published that all pregnancies qualify by risk
benefit
analysis.[2]. Now it is even more true.
First
trimester risk estimation may ultimately lead to detection of 80% of
trisomy 21
and 80% of trisomy 18 after indicated diagnostic testing.
This is less than half of the chromosome
abnormalities which may be present with advanced maternal age. Second Trimester ultrasound (often called
genetic sonogram by non-geneticists) will falsely reassure about half
of
chromosomally abnormal pregnancies. The
popularity of risk reduction for advanced maternal age is flawed by the
fact
that the presence of an abnormal finding is very important but the
absence of
an abnormal finding is not equally reassuring. There
is already a rising incidence of
chromosomally abnormal newborns born
to couples who were falsely reassured by screening.
It may be too early to officially propose
eliminating all
“screening” and simply offer amniocentesis to everyone. This would be
the most
cost effective and is the likely eventuality. But
for now, if we adopt the British 1st trimester
approach for low risk patients we should not apply it to advanced
maternal age
patients. Any approach to avoid “the
needle” eventually deprives the patient of the correct answer in half
the
abnormal pregnancies. This popular but
deleterious path should be abandoned. That
will automatically occur when
patient autonomy is respected by
giving true informed consent about risks, benefits, accuracy
and
limitations of screening and diagnosis. Counseling
and consent will be the basis
of all liability questions.
I
believe it is an error to dissuade a patient from amniocentesis. That now includes even a low risk
patient. Risk
estimation of any sort should not be held out as a
replacement or even a logical alternative to amniocentesis. This will be debated ad infinitum but it is
actually no longer even worthy of discussion. Amniocentesis
should always be
encouraged-never discouraged.
Please
contact Dr. Henry's office at 303-399-5393 if you have
any questions. Ask to speak to a Genetic Counselor.
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