Amniocentesis is an important way of finding
out how a baby is developing while inside
the womb, including whether it may develop
a genetic disorder.Routine amniocentesis is
recommended for women over 35. At that age
the risk of the procedure causing a miscarriage
is about the same as the risk of the fetus
having Down's syndrome. In other cases amniocentesis
is done if there is any special reason to
suspect trouble. The risk of causing miscarriage
by amniocentesis is about 1 per cent. That
means that about one woman in every 100 having
an amniocentesis will suffer a miscarriage.
Why it should
be done
Amniocentesis is a
method of detecting serious or potentially
serious disorders in the unborn child.It
gives parents the option of deciding whether
or not they want to have a child that will
have one of these disorders, or whether
they would prefer the pregnancy to be terminated
at that early stage. It also sometimes provides
the opportunity for early treatment of the
disorder while the fetus remains in the
womb.
Why it is
necessary
Amniocentesis provides
direct information about the likelihood
or certainty of the baby developing one
of a number of conditions. Disorders that
can be detected or strongly suspected following
amniocentesis include:
- Rhesus factor disease
- Congenital absence
of the brain (anencephaly)
- Respiratory distress
syndrome
- Congenital defects
in the spinal cord and column (Spina bifida)
- Down's syndrome
- Cystic fibrosis
- Haemophilia
- Duchenne muscular
dystrophy
- Thalassaemia
- Sickle-cell anaemia
- Antitrypsin deficiency
- Phenylketonuria
The amniotic fluid
in which the fetus floats always contains
cells cast off by the fetus. Those cells
that are obtained by amniocentesis can be
cultured in the laboratory so that chromosomes
can be checked two or three weeks later.
In this way a range of genetic diseases
can be diagnosed before birth.
How it is performed
An area of the abdominal
(tummy) wall is anaesthetised with a local
injection. Ultrasound scanning then ensures
that a needle can be passed safely through
the walls of the abdomen and womb into the
amniotic fluid in which the fetus is floating.
A sample of fluid can now be sucked out
with a syringe.
Because this fluid
contains cells shed from the skin of the
fetus and various substances secreted by
the fetus, the samples obtained can be very
important for diagnosis. Every fetal cell
contains a complete set of the DNA of the
fetus.
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Amniocentesis
