here - Health Promotion Agency

Antenatal care and antenatal classes
T ESTS TO DETECT ABNORMALITIES
IN THE BABY
It is important to realise that no test
can guarantee that your baby will be
born without abnormality. No test is
100% accurate and some abnormalities
may remain undetected.
The tests below are designed to
detect structural abnormalities like
spina bifida or genetic disorders like
Down’s syndrome. Down’s syndrome
is caused by an abnormal number of
chromosomes. Chromosomes are the
structures within every cell of a person’s
body which carry the individual
genetic code or recipe to make that
person. Conditions like cystic fibrosis
and achondroplasia (dwarfism) are
caused by abnormalities within the
chromosomes (so causing a ‘mistake’
in the recipe). Talk to your midwife,
GP or obstetrician about the tests
mentioned below as they are not
available in all hospitals.
When you are deciding whether
or not to have a test, think what you
might do if the test suggests that
your baby has an abnormality. If a
screening test (serum screen or
nuchal translucency) suggests a high
risk of genetic abnormality, you will
be offered amniocentesis or
chorionic villus sampling (CVS) to
give a definite diagnosis. Since these
carry a risk of miscarriage, you may
decide not to have these tests or even
a screening test if you would choose
to continue with the pregnancy.
Having a test, however, may reassure
you that your baby is likely to be
born healthy, allow you to consider
the termination of an affected baby
or give you time to prepare for the
arrival of a baby with special needs.
Tests can also provide valuable
information for your care during
the pregnancy. Discuss the issues
with your partner, midwife, doctor
and friends.
ULTRASOUND (see also page 56)
Since ultrasound provides an image
of the baby in the womb, it detects
structural abnormalities, particularly
of the spine and head. Recently,
however, it has been found to be
useful in screening for Down’s
syndrome and some other
abnormalities of chromosome
number. Several research studies
have shown that the thickness of
‘nuchal fold’ at the back of the baby’s
neck is related to the risk of Down’s
syndrome. An ultrasound scan at 11
and 14 weeks enables a measurement
to be taken. This measurement then
allows a risk factor to be calculated.
The nuchal translucency scan is not
widely available at present but it is
becoming more so.
ALPHA-FETOPROTEIN (AFP) TEST
This test is performed at about
15–20 weeks to find out the level of
alpha-fetoprotein (AFP) in your
blood. This protein is made by your
baby and passes into your blood
during pregnancy. High levels are
associated with spina bifida, so an
ultrasound scan will then be offered
to check for this. High levels may be
seen in normal pregnancy
and also in twin
pregnancy. Low levels of
AFP are associated with
Down’s syndrome
pregnancies. Ultrasound
and amniocentesis will
then be suggested to
achieve a diagnosis.
Some hospitals routinely offer the
AFP test to all women; others don’t,
or restrict the test to older women,
since the risk of Down’s syndrome,
and some other abnormalities of
chromosome number, increases
with age.
IF A TEST DETECTS AN
ABNORMALITY,
you may like to contact the
appropriate organisation
(see page 147–50) for
further information. They
may be able to put you in
touch with parents who have
decided to continue with a
pregnancy in which an
abnormality has been
detected. ARC (Antenatal
Results and Choices; see
page 149 under ‘Loss and
Bereavement’) will offer
support and information if
you are considering
termination for abnormality.
Abortion law in England,
Wales and Scotland is
governed by the Abortion
Act 1967, as amended by
the Human Fertilisation and
Embryology Act 1990. The
Abortion Act 1967 does not
extend to Northern Ireland,
and the grounds on which
abortion may be carried out
in Northern Ireland are,
therefore, more restricted
than those in Great Britain.
57