What is an amniocentesis?
Amniocentesis is a
procedure used to take a small sample of the
amniotic fluid that surrounds a
fetus. Amniotic fluid contains cells and waste
products from the fetus that can give clues about the fetus's health. The
procedure is done by inserting a needle through your abdomen into the
2Tbsp of the amniotic
fluid is drawn out and then tested in a laboratory. Amniocentesis is done
between weeks 15 and 20 (usually around week 16) of pregnancy.
Genetic testing of the amniotic fluid sample can detect fetal problems
Down syndrome and
neural tube defects. It can also detect more than 100
types of family diseases such as
sickle cell disease, and
Huntington's disease. A fetus's sex can also be
identified by testing the amniotic fluid.
How would I use amniocentesis results?
results from an amniocentesis suggest that a fetus has normal chromosomal
formation and no markers for neural tube defects. Although this is reassuring,
it does not guarantee that a baby will be born completely healthy-no single
test can find all possible problems.
If abnormal test results
tell you that your fetus has a birth defect, you can make informed, if
difficult, decisions. The decisions you are faced with depend on various
factors. These include the specific type of defect involved and your own and
your partner's preferences. For example, you may want to consider:
- Whether to continue the pregnancy. If a fetus has a severe
defect, some women choose to end the pregnancy (have a therapeutic abortion).
Others want time to prepare themselves and their families for the birth of a
child who has a birth defect.
- Where to have the baby. If the fetus has a defect that will
require surgery, it is best to deliver at a hospital that offers surgical
services for newborns.
- Whether to have a vaginal delivery or to plan a
cesarean delivery (C-section), based on the fetus's
If there is a need for a C-section or early delivery, the
results from an amniocentesis can be used to see if the fetus is mature enough
Is there another type of test I can have instead of amniocentesis?
If you are still in your first trimester, you can
consider chorionic villus sampling (CVS) as an alternative to amniocentesis.
CVS can detect Down syndrome and genetic diseases earlier in pregnancy than
amniocentesis. But CVS cannot detect a neural tube defect.
recent study showed that both tests have a similar risk of miscarriage. In that
study, the miscarriage risk was about 1 in 400, with the tests being done by
highly trained providers.1 Some studies have shown
higher miscarriage risks, between 2 and 4 in 400. This greater risk may be more
likely in medical centers with less experienced providers, especially for
CVS.2 The risk of miscarriage with CVS may be smaller
when the procedure is done through the abdomen than when it is done through the
cervix.3 For more information, see the medical test
Chorionic Villus Sampling (CVS).
What are the risks of amniocentesis?
is usually very safe. In a pregnancy for which amniocentesis is recommended,
the benefit of knowing whether the fetus has a birth defect, inherited disease,
or Down syndrome is typically greater than the risk of having the procedure.
But there are some risks, including:
- Injury to the mother or fetus from the needle. Using ultrasound
to guide the needle reduces this risk. The most common injury is puncture of
placenta, which usually heals without a
- A less than 1-in-1,000 risk of causing an infection by
introducing bacteria into the
- Miscarriage. One study showed that amniocentesis has a
1-in-400 chance of causing a miscarriage when done by a highly trained
doctor.1 In some studies, the risk is a little higher,
about 2 to 4 in 400.2 (Some miscarriages after
amniocentesis are not linked to the procedure. Instead, they are caused by a
problem with the fetus or pregnancy.)
- A slight risk that the mother will be exposed to the fetus's
blood during amniocentesis. This is only a concern if your blood is Rh-negative
and you are at risk of
Rh sensitization. If so, sensitization can be
prevented with a vaccine given after the test.
- An increased risk that the fetus will develop
clubfoot when amniocentesis testing is done early,
before 15 weeks of pregnancy.
What are the risks of not having an amniocentesis when one is recommended?
If you don't have prenatal diagnostic testing, you
could potentially give birth to a baby with an undiagnosed birth defect or Down
- Such a birth can be more complicated and risky to the baby when
a doctor is not expecting newborn health problems.
- You could give birth in a hospital that does not have a
neonatal intensive care unit (NICU) for sick or premature newborns.
- A fetus with a very rare, severe defect sometimes dies before
- Many parents are emotionally ill-prepared for the sudden birth
of a baby who is sick or has a birth defect.
Talk to your health professional about all available
Should I consider an amniocentesis at all?
Amniocentesis is not used for routine early pregnancy screening because
it carries some risks. Common reasons for electing to have an amniocentesis
- Abnormal results from a
maternal serum triple or quadruple screen or a
screening test done in the first trimester, suggesting that your fetus
may have a birth defect or Down syndrome.
- Fetal ultrasound imaging suggesting the presence of a
- Family history of birth defects, such as a neural tube
- Parent (you or your partner) who is a carrier of an inherited
disease, such as
Tay-Sachs disease or sickle cell disease.
- A need to know the fetus's sex. This is important when a parent
is a carrier of a sex-specific disease, like
Duchenne muscular dystrophy. Both of these diseases
occur mainly in males.
For more information, see the medical test
Fetal Ultrasound or
Birth Defects Testing. For more information about the
triple or quad screen, see:
- Maternal serum triple or quadruple screen.
- Alpha-Fetoprotein (AFP) in Blood.
- Human Chorionic Gonadotropin (hCG).
- Hormone Inhibin A.