Normal amniotic fluid is
clear to light yellow in color and does not contain any harmful bacteria. The
cells can be tested for problems.
Cells from your fetus are looked at carefully
for the proper number and arrangement of the cell parts (chromosomes) that show genetic disease. Normally there
are 46 chromosomes in each cell, arranged in 23 pairs. Chromosomes also tell
the gender of your fetus.
The amounts of some substances in the
amniotic fluid may be measured. These results can find some birth defects,
genetic diseases, and the maturity of your fetus.
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
If there is blood from your fetus in the amniotic fluid. This can
falsely increase the level of the substances alpha-fetoprotein (AFP) and
acetylcholinesterase (AChE) levels, which test for
neural tube defects.
If the amniotic fluid
is exposed to light. This can falsely lower bilirubin levels.
there is blood or meconium in the fluid. This may cause an incorrect result for
the test that checks to see whether your baby’s (fetus’s) lungs are
What To Think About
Normal results from amniocentesis do not
guarantee that your fetus will be healthy.
Amniocentesis is not done as a general screening test for birth
defects, because it has some risk to your fetus and cannot find some common
birth defects. There is a chance (about 1 out of 400) that this test may cause a
miscarriage.1 In some studies, the risk is a little
higher, about 2 to 4 out of 400.2 Amniocentesis can be
done to help you prepare if your fetus has a possible birth defect or to help
you make a decision about ending the pregnancy if a serious problem is found.
For more information about amniocentesis in early pregnancy, see:
In very rare cases, amniocentesis may be done before 15 weeks of pregnancy. This is rare, because there may be greater risks to your fetus. Talk to your doctor about the risks and benefits of early amniocentesis.
Amniocentesis cannot be done easily if the amount of
amniotic fluid is very small or if the placenta is in front of your
Chorionic villus sampling (CVS) is another test that
can find many fetal problems. CVS can be done earlier in pregnancy (at about 10
to 12 weeks) than amniocentesis, and results are ready sooner. It can find more
than 100 genetic diseases. One study showed that CVS also has about a 1-out-of-400
chance of miscarriage when it is done by a highly trained provider.1 CVS cannot be used to find neural tube defects. For more
information, see the topic
Chorionic Villus Sampling (CVS).
Amniocentesis has a very small
chance of causing bleeding that could lead to mixing your blood and your
fetus's. So if you have Rh-negative blood, you will be given a vaccine (RhoGAM)
to prevent Rh sensitization, which could harm your fetus if he or she has
Amniotic fluid has cells that have been shed by
your developing fetus. The cells are checked for the number and size of
chromosomes (karyotype) to see if there are any problems. For more information,
see the topic
If you have abnormal results from amniocentesis, you should ask
your doctor or a
genetic counselor for help in making decisions about
the problems your fetus may have and about continuing the pregnancy. It will
also be helpful to understand your possible risks with future