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. Different
maternity units may use different
tests, but all tests should meet
national standards.
The ultrasound and alphafetoprotein
(AFP) test may detect
structural abnormalities like spina
bifida or some chromosomal
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 chromosomal 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 can
detect structural abnormalities,
particularly of the spine and head. It
can screen for Down’s syndrome and
some other abnormalities of
chromosome number. Studies
have shown that the thickness of the
nuchal pad at the back of the baby’s
neck is related to the risk of Down’s
syndrome. A nuchal translucency
scan is an ultrasound scan at 11 and
13 weeks that enables a measurement
to be taken. This measurement then
allows a risk factor to be calculated.
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 combined with levels of other
biochemical markers are associated
with Down’s syndrome pregnancies.
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’) helps
parents with all issues
associated with antenatal
testing and its implications.
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