Amniocentesis (AMNIO)
Prior to amniocentesis you will discuss the test with one of the genetic counselors. The counselor will review
your pregnancy history and your family histories to determine if you and your partner have any special risks
for having a child with a genetic disease or birth defect. The counselor will also review the screening and
testing options available to you. The counseling that will be provided uses an approach that is called “nondirective”. That means that the counseling is intended to provide you with the information that you will need
to make the best decision for you and your family. The counselor does not make specific recommendations
about whether to have a test, because the decision is influenced by very personal values.
Amniocentesis is a procedure in which a needle is introduced through the skin of the abdomen into the
uterus in order to withdraw a small amount of the amniotic fluid (water) that surrounds the fetus. The
procedure is performed in the doctor’s office. Ultrasound is used to evaluate the pregnancy and to help
determine where to insert the needle. Usually, the needle that is used is the same or slightly thinner than a
needle that might be used to draw your blood, but it is longer in order to reach the fluid in the uterus. During
the insertion of the needle ultrasound is used to guide the placement of the needle. Prior to the needle
insertion you skin will be prepped with an antiseptic solution and the sterile technique will be used to reduce
the chance of introducing bacteria (germs) into the uterus. Some women mistakenly believe that the needle
is inserted into the mother’s umbilicus (belly button). The needle is never inserted into the mother’s
umbilicus. The insertion of the needle is associated with discomfort like any other needle that is inserted
through the skin and the tissues beneath the skin. Once the need is in place the mother usually does not
feel discomfort during the collection of fluid or the removal of the needle. Less than an ounce of amniotic
fluid will be removed. The fetus and placenta replace this fluid within several hours. It usually takes less
than a minute to draw the fluid into the syringes. After the procedure you will be asked to verify the labels on
the test tubes in which your amniotic fluid has been placed and you will be given printed instructions. No
special dressing or care of the puncture site is needed. Most women return to the normal activities following
amniocentesis.
Amniocentesis is considered to be very safe for the woman and her pregnancy. Although the risks are low,
the possible complications of this test are important. There is a risk that amniocentesis can cause a woman
to miscarry. In the past it has been estimated that amniocentesis might cause miscarriage in less than one
out of every two hundred pregnancies tested. More recent studies suggest that the risk of the test causing
miscarriage is much lower, perhaps less than one out of every five hundred or one thousand procedures.
About one or two percent of women who do not have amniocentesis will miscarry after sixteen weeks of
pregnancy. Because of this higher "natural" rate of miscarriage, it has been concluded that most
miscarriages following amniocentesis are not due to the procedure. When a woman has this test, and then
miscarries, it usually cannot be determined if the miscarriage was due to the test or if this was one of the
pregnancies that would have been lost without the test having been performed.
There is also a chance that amniocentesis will cause an infection in the uterus and that this will result in
miscarriage. This happens so rarely that it is difficult to estimate the exact rate at which this complication
occurs. Although a rare complication of amniocentesis, infections in the uterus during pregnancy can
progress rapidly and become very serious. Very rare cases of shock and even death have been reported
associated with infection of the uterus and pregnancy.
In addition to antibiotics, termination of the
pregnancy is often necessary to effectively treat these infections before serious complications occur. The
printed instructions will tell you how to watch for infection and other possible complications of the test.
Most women are concerned about whether the amniocentesis needle may injure the fetus. This is also
extremely rare, and the injury is usually so minor, that it is also difficult to estimate the exact rate at which
this complication occurs. When this occurs, there may be only a very minor mark or scar on the skin of the
baby. These may be difficult to distinguish from naturally occurring skin marks, and are usually not
cosmetically significant. It is possible for a baby to have a cosmetically significant scar or even a serious
internal injury, but this is very, very rare. Only a few such cases were reported before the use of ultrasound
guidance and millions of amniocenteses have been performed worldwide. Thus, it is believed that a serious
injury is a very rare event.
Another risk of amniocentesis is the possible development of an Rh problem if the woman is Rh-negative.
To prevent this problem from developing, an injection of Rh immune globulin(RhoGam) is given just after the
amniocentesis if the mother is Rh-negative. This is the same safe and effective medication which is given to
women who are Rh-negative after they deliver a baby that is Rh positive.
Because doctors are experienced with the test, they can usually get fluid from the uterus on the first attempt.
Infrequently, a second needle insertion is required. Sometimes it is better to wait a few days or a week
before a second attempt is made. At that time, the test is almost always successful. Once we have obtained
an adequate fluid sample, the chances are very good (greater than 99%) that we will be able to complete the
test for you. Occasionally, it is necessary to repeat the procedure if the cells do not grow in the laboratory or
if the interpretation of the results is not clear. If this occurs, a repeat test or alternative testing will be offered
to you. As previously mentioned, it usually takes about two weeks before the final test results are available.
Because the completion of the test is dependent on the growth of cells in the laboratory, the test may be
completed a few days earlier or it may take a few days longer. You will be notified as soon as the results
are available.
Many patients have testing for reassurance because they know it is likely that the test results will be normal.
During your counseling, our genetic counselors will have reviewed the options available to you if your tests
results are abnormal. If the results of your test are abnormal you will also be provided with “non-directive”
counseling to help you make decisions about your pregnancy, When the fetus has a serious birth defect that
cannot be corrected, you may choose to terminate the pregnancy. Although pregnancy can be safely
terminated as late as 20 or 22 weeks from the last menstrual period, it can be a difficult situation from an
emotional point of view. At that time in pregnancy, the risks of pregnancy termination are about the same or
less than they are for women who deliver at term. Some patients who learn that their fetus has a problem
decide to continue the pregnancy. They often find the information from the test useful to help them learn
about the disorder and to prepare for the birth of the child with special needs.
It is also important to know about the accuracy of these tests. The chromosome test that will be performed
on the amniotic fluid sample is 99% accurate to detect Down syndrome. It is also highly accurate to detect
other chromosome disorders in which there is an extra or missing chromosome in every cell of the body. We
also routinely offer testing on the same fluid sample for a condition known as spina bifida (open spine
deformity). Spina bifida occurs in about one out of every one thousand babies, and is often a very disabling
condition. Although you may not have a special risk for having a child with spina bifida, this test can be
performed on the liquid portion of the sample (as opposed to the cells that will be used for chromosome
testing).. Testing for spina bifida and for other chromosome problems is also very accurate (more than 90%).
Even if you have normal results from an amniocentesis, it is usually recommended that you also have an
ultrasound at about twenty weeks of pregnancy for an examination of the fetal anatomy.
It is important to realize that although there is a large number of different genetic diseases, and chromosome
disorders that can be diagnosed by amniocentesis, there are only a limited number of tests that are routinely
performed on one fluid sample. Which testing to perform is usually based on your individual risks for having
a child with a particular genetic problem. Therefore, other genetic diseases or disorders may be present for
which we do not perform a test on your amniotic fluid sample. Also, there are many other birth defects and
genetic diseases and disorders that cannot be detect accurately by amniocentesis or by ultrasound. For
these reasons, having amniocentesis and/or ultrasound does not guarantee we have checked for every
disease or disorder that can be detected by this procedure. Although no combination of tests can guarantee
a normal child, amniocentesis and ultrasound can significantly reduce you risk of having a child with certain
common birth defects and genetic problems.
We hope this information is useful to you in making your decision about amniocentesis.
Michael M. Mennuti, M.D.