Amniocentesis
Amniocentesis is a
diagnostic test that may be recommended by your healthcare provider after an
abnormal triple test. Hereditary or genetic problems lead some parents to opt
for an amniocentesis to determine if their child may have certain genetic
disorders.
How is amniocentesis performed?
The ultrasound is
used as a guide to determine a safe place where the needle can enter the
amniotic sac so that the fluid can be safely removed. A sample of amniotic
fluid is taken through a needle. The procedure takes about 45 minutes, although
the collection of fluid takes less than five minutes.
Amniotic fluid
containing cells secreted by the fetus is sent to a laboratory for analysis. It
may take from several days to several weeks to receive results.
When is an amniocentesis performed?
Amniocentesis is
usually done between 14 and 20 weeks. Some medical facilities can perform
amniocentesis as early as 11 weeks.
Amniocentesis may be
used later in the third trimester for several reasons. Your doctor may
recommend this procedure if you have premature rupture of membranes to evaluate
for uterine infections. Amniocentesis can also help determine the severity of
fetal anemia in children with Rh and help your doctor determine if the fetus
needs life-saving blood transfusions.
Amniocentesis is
sometimes done to assess lung maturity. If yes, then this is done shortly
before delivery.
What does an amniocentesis test look for?
Amniocentesis detects
chromosomal abnormalities, neural tube defects, and genetic disorders. Down
syndrome or trisomy 21 is the most common chromosomal abnormality. Genetic
disorders include disorders such as cystic fibrosis. The most common neural
tube defect is spina bifida.
Amniocentesis is
sometimes used late in pregnancy to assess whether the baby's lungs are mature
enough for the baby to breathe on its own.
Amniocentesis also
provides access to DNA to verify paternity before delivery. DNA is taken from
the potential father and compared with the DNA obtained from the child during
the amniocentesis. The results are accurate (99%) in determining paternity.
What do the results of an amniocentesis mean?
Amniocentesis is a
diagnostic test that detects chromosomal abnormalities, neural tube defects,
and genetic disorders with high accuracy (98-99%). Although the chances of
identification are high, this test does not measure the severity of these birth
defects.
Alpha-fetoprotein
levels and advanced ultrasound can help assess the degree of disability that
may be present.
What are the risks and side effects for the mother or baby?
While amniocentesis
is considered a safe procedure, it is recognized as an invasive diagnostic test
with potential risks. Miscarriage is the main risk associated with
amniocentesis.
The risk of
miscarriage ranges from 1 in 400 to 1 in 200. In facilities where amniocentesis
is performed regularly, the rate approaches 1 in 400. Miscarriages can occur
due to uterine infection, fluid loss, or premature birth.
Although this is
extremely rare, the needle may come into contact with the baby. Great care is
taken to use the sonogram to keep the needle away from the child. The mother
may feel sharp pain when the needle is pierced under the skin and again when
the needle is inserted into the uterus.
After the procedure
is completed, the mother may experience other side effects, including:
- Cramping
- Leakage of fluid
- Minor irritation around the puncture site
- Contact your doctor if these complications continue or get worse.
What are the reasons to test or not to test?
Reasons for testing
or not testing vary from person to person and couple to couple.
Performing tests and
confirming the diagnosis gives you certain options:
- Pursue potential interventions that may exist (i.e. fetal surgery for spina bifida)
- Begin planning for a child with special needs
- Start addressing anticipated lifestyle changes
- Identify support groups and resources
Some individuals or
couples may refuse to be tested or additional tested for a number of reasons:
- They are comfortable with the results no matter what the outcome is
- Because of personal, moral, or religious reasons, making a decision about carrying the child to term is not an option
- Some parents choose not to allow any testing that poses any risk of harming the developing baby
It is important to carefully discuss the risks and benefits of testing with your doctor. Your doctor will help you evaluate whether the benefits of the results may outweigh the risks of the procedure.