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come home with you. In the morning
you can hardly remember how it felt
to simply enjoy your pregnancy. Your
belly has become a heavy weight that
you find yourself supporting as you go
through that difficult day.
Welcome to the brave new world of
prenatal diagnosis, where we are given
information that is unprecedented in
human history, and choices that can be
as painful as they are complex. Prenatal
diagnosis — the detection of abnormalities
of babies still in the womb — is driven
by the increasing expertise of medical
technology, but it is clearly sanctioned
by our society; most people in Australia
support abortion when there is a major
abnormality. 1 It seems that we have
decided, collectively as well as individually,
that we want to avoid the difficulties
of raising children with disabilities
— especially, in our society, with intellectual
disabilities. However, for prenatal
diagnosis to contribute to this end,
some of us must choose to terminate our
wanted pregnancies.
Pandora’s Box
Prenatal diagnosis can open a veritable
Pandora’s Box for the woman and her
family, and also raises wider, profound,
ethical and philosophical questions. For
example, how can we call ourselves a
tolerant and inclusive society — a society
that celebrates difference — when we
have an entire industry directed towards
eradicating babies who have obvious
differences? And our values are portrayed
very starkly when we specifically
target babies with Down syndrome, a
condition that is not usually fatal, but
is associated with intellectual disability
and with characteristic physical features
that our society does not recognise as
beautiful.
Some of the personal impact of prenatal
testing is illustrated in the story
above. Whether this baby is affected
(1 in 300 chance, in this scenario) and
aborted; is affected and kept (which is
very rare); miscarries as a result of the
procedure (about 1 in 100 chance with
amniocentesis) or is born healthy (299
chances out of 300, without amniocentesis),
the mother has been through a
difficult process. Most women who opt
for these tests are unaware that they are
entering an emotional minefield, with
consequences that may last for years.
Many are also unaware that the tests
that they are accepting will not detect
all, or even most, abnormalities in their
unborn babies.
Recent Australian research also
shows that the majority of pregnant
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women are not well informed before
or after they undergo tests for prenatal
diagnosis. 2,3 In a UK study, nearly half
of the obstetricians surveyed felt that
they did not have adequate resources
for all the women to whom testing was
offered. 4
Screening vs diagnostic tests
Our mother-to-be has accepted a Down
syndrome screening test for her baby.
Like 1 in 20 of the women who opt for the
second trimester maternal serum screen
(STMSS) — a blood test at 15 to 18 weeks
— she received a ‘screen positive’ result,
with all the anxiety that accompanies
this news. However, only around 1 in 50
women who test positive will actually
have an affected baby; the remaining 49
have had ‘false positive’ results. As well
as this, with a detection rate of 60-70%,
STMSS will fail to detect around 1 in 3
babies with Down syndrome. Detection
rates for spina bifida, the other major
condition that may be discovered with
STMSS, are around 70%, which means
that, similarly, 1 in 3 affected babies will
not be detected with this test. 5
Why is this widely used test so inaccurate?
The major reason is that it is not
a diagnostic test — that is, it can’t give
a definite diagnosis for the baby. It is
a ‘prenatal screening’ test, designed to
give an indication of risk so that the next
step — a diagnostic (and invasive) test of
the baby’s cells by amniocentesis or chorionic
villus sampling (CVS) — can be
targeted to women who are more likely
to be carrying an affected baby. Limiting
these diagnostic tests is sensible, because
they carry their own risks; especially of
causing a miscarriage. Termination of
pregnancy is also not without risk to the
mother, especially when it is a late termination
(after 3 months or so) because
it usually involves inducing labour with
drugs.
These prenatal screening tests have
been promoted as a ‘no-risk’ test to
women (especially younger women)
who may not consider themselves likely
to have a baby with Down syndrome,
and may not consider invasive testing,
because of the risk of miscarriage.
For example, women aged under 35
have a generally low chance of giving
birth to an affected baby, but, because
most babies are born to these younger
women, so will most babies with Down
syndrome. Screening tests can tell an
individual woman whether she has a
higher chance of carrying an affected
baby, and she can be offered a diagnostic
test when her risk is over 1 in 250 to 300.
This is approximately double the normal
risk, as approximately 1 in 600 women
give birth to a live baby with Down
syndrome. In this way, screening tests
increase the overall numbers of Down
syndrome babies detected and aborted
because around 70% of Down syndrome
babies are born to women under 35.
There are two other screening tests
that are increasingly used in Australia
and overseas. The first is an earlier blood
test, performed at around 10 weeks and
known as first trimester maternal serum
screening (FTMSS). FTMSS analyses
different components of the mother’s
blood and has, in some studies, given
as accurate results as STMSS, although
it cannot detect defects like spina bifida.
The second early prenatal screening test
is a specialised ultrasound, which measures
the thickness of the skin fold at
the back of the baby’s neck at 11 to 12
weeks. This is known as nuchal translucency
(NT) testing. Babies with Down
syndrome, and several other less common
abnormalities, are likely to have a
thicker skin fold at the back of the neck.
As with all screening tests, most babies
who test positive on NT will actually be
normal.
Early detection, early relief?
These new, early tests are believed
to benefit women because the whole
process (screening, diagnosis and
possibly termination) can then take
place at an earlier stage of pregnancy,
perhaps even before the woman has
shared her news. CVS, as a diagnostic
test, can be performed from 10 weeks,
and a termination, if chosen, can also be
done at this earlier stage of pregnancy.
However, studies show that, because
of the complexity of these procedures
and the time needed to make these
major decisions, many women who
have had a FTMSS do not actually have
a termination until after 16 weeks. 6
The complexity of prenatal screening
is increasing because researchers are
looking at different combinations of
FTMSS, STMSS and NT. Currently
the best figures for detection of Down
syndrome are produced through
‘integrated testing’, which detects over
75% of affected babies with a false
positive rate of 3%. Integrated testing
involves FTMSS at 10 weeks, NT at 10 to
12 weeks then the 14-week STMSS. When
all these results are back (a long wait),
the woman will receive her risk estimate
and she can then decide whether she
wants to proceed with amniocentesis.
The UK government has pledged
to make this test available on NHS
in 2007, and it is very possible that