Author: Craig V. Towers M.D., F.A.C.O.G
- Describe how the amniocentesis procedure has changed over the years and the best approach currently for performing the procedure to minimize complications.
- Explain the various risks and complications associated with amniocentesis.
- Explain the significance of brown colored fluid that may be obtained at the time of genetic amniocentesis and the use of amniocentesis in Rh negative women.
- Describe how intra-amniotic bleeding that can occur at the amniocentesis site, may appear sonographically.
Introduction and History:
The first amniocentesis procedures
were reported by Von Schatz, Lambl, and Prochownick in the 1870’s and early
1880’s. These early procedures were used
to relieve patients that were suffering from severe polyhydramnios. In 1930, Menees reported performing the
procedure on pregnant women for the purpose of amniography.
The main focus of the amniocentesis changed to that of a
diagnostic procedure in the mid 1950’s.
These early procedures were for fetal gender determination based in part
on the research of the Canadian anatomist, Murray Barr, who described the “barr
body” in 1949. When more than one
X-chromosome is present, one is usually active and the other is inactivated. The inactivated X-chromosome forms a
chromatin mass called a barr body. The
sex chromosome makeup for females is two X’s and for males is an X and a
Y. Therefore, females will have a barr
body and males do not. In 1956, Fuchs
and Riis reported performing amniocentesis procedures to determine fetal sex by
analysis of the presence or absence of the barr body.
In the mid 1960’s, Steele, Bregs, and Nadler described the
performing of amniocentesis procedures in order to culture cells for a full
chromosome analysis and also the measurement of alphafetoprotein (AFP). Hence the birth of the genetic
amniocentesis. Since the late 1960’s,
amniocentesis has become a very common obstetrical procedure, not only for genetic
evaluation, but also for diagnosing other issues such as infections, fetal
maturity, relieving polyhydramnios, and in analyzing Rh sensitized women.
The Risks of amniocentesis:
From a statistical point of view,
amniocentesis is a very safe procedure with an overall complication rate that
is very low (usually less than 1%).
However, the complications that might occur can be devastating to a
family such as injury to the fetus or loss of the pregnancy. Therefore, the procedure should never be
taken lightly. The pregnant couple
should understand the reason why they might have the procedure performed and
agree to having it done. This is
especially true for pregnancies that have not reached viability (such as the
majority of genetic procedures).
The complications related to
amniocentesis include pregnancy risks of rupturing the membranes, causing
bleeding, and introducing infection – all of which might result in the loss of
the pregnancy. The fetal risks can
include trauma from the needle and/or death (primarily due to the pregnancy delivering
prior to viability), while the maternal risks reported have included
intra-abdominal infections, sepsis, amniotic fluid embolus, and endometriosis
in the needle track.
The majority of reports on fetal
trauma have described scars or markings on the skin of the limbs and torso;
however, there have been case reports of central nervous system bleeds, ocular
damage, and laceration of intra-abdominal organs. The majority of these case reports have
occurred prior to the use of ultrasound as an aid in performing the
procedure. Yes, believe it or not, in
the late 1960’s and early 1970’s amniocentesis was performed blindly without
the use of ultrasound.
The main concern in performing
amniocentesis is a complication that results in the delivery of the
pregnancy. In regard to amniocentesis,
pregnancy can be divided into 3 or 4 time periods that each have a different
set of circumstances. These categories
are the term or near term pregnancy (> 34 weeks gestation), the
previable pregnancy (< 23 weeks gestation) and the potentially viable but
premature fetus (which is 23 to 34 weeks gestation and this category might be
divided into the significantly premature 23 weeks up to 30 weeks and the
moderately premature 30 to 34 weeks gestation).
If a patient is term or near term (> 34 weeks
gestation) and the procedure is performed for fetal maturity, or to relieve
polyhydramnios, or to diagnose infection and the membranes rupture, this might
result in the delivery of a baby that needs intensive care therapy for
delivering somewhat early. However, in
most cases the child will survive and develop normally barring any unforeseen
congenital problems. If the procedure is
performed in the previable gestational age and the pregnancy delivers, it is
lost, which can be difficult for some pregnant couples to handle emotionally,
but the tragedy ends. The most difficult
time period to deal with is the viable pregnancy that is significantly
premature (23 weeks up to 30 weeks gestation); because the child can survive
but might have long term sequelae related to prematurity if delivered. The gestational age of 30 to 34 weeks is more
controversial. Neonatal intensive care
therapy has greatly improved over the years and the majority of these neonates
do well. However, their risk is still
higher than a pregnancy that goes beyond 34 weeks gestation. Therefore, all pregnant women who decide to
have an amniocentesis need to have good informed consent but the issues
involved will differ depending on the gestational age.
The majority of studies that have analyzed the pregnancy loss
rate related to the procedure have focused on the genetic amniocentesis
performed prior to viability or less than 23 weeks gestation. When evaluating these studies, multiple
factors come into play including the use of ultrasound and how ultrasound is
utilized, the gauge of the needle, experience of the performer, fluid color,
the number of procedures required in order to obtain enough fluid,
transplacental approach, and maternal history.
Another difficulty that is encountered when looking at the
various studies is how “a pregnancy loss” was defined. There are well over 50 studies in the
literature that have analyzed the loss rate following amniocentesis. Some of these have compared the survival rate
all the way up to 7 days after delivery, whereas others have analyzed the loss
rate up to 28 weeks gestation. Still
others have only compared the loss rate up to 24 weeks or only within 1 to 4
weeks following the procedure. As you
can, it is difficult to determine the true definition of a loss following the
procedure. In addition, some of these
studies only report their outcome with no comparison or controls. Furthermore, nearly all of them are
retrospective meaning that the data was collected at a later date.
To compare the loss rate differences all the way to delivery
including the first 7 days of life of the newborn between pregnancies that had
an amniocentesis versus those that did not seems quite long. This brings into play the differences in how
pregnancies were handled once viability was reached and may not be a true
indication of the actual risk of the procedure.
If one analyzes only the prospective controlled studies that evaluated
the loss rate up to 28 weeks gestation, the difference between the two groups
(those with amniocentesis versus those without) is about 0.4% to 0.5% which is
1 in 200 to 1 in 250. This risk of 1 in
200 to 1 in 250 is probably the most often used risk rate quoted for
amniocentesis and was the rate found in the United States Collaborative study.
Many other studies are in print that have listed loss rates
ranging from 1 in 150 to 1 in 500, but again, most of these are retrospective
without controls and vary on the use of ultrasound, experience of the
performer, the needle size, and number of attempts. Currently there is only one prospective
randomized study on genetic amniocentesis and this will probably never be
performed again for ethical reasons. The
study by Tabor, et al, was published in 1986 and involved 4,606 low risk women ages
25 to 34 who were randomized to have a genetic amniocentesis versus no
amniocentesis and the loss rate difference was 1 in 100 or 1%. The original study reported the use of an 18
gauge needle but this was later described as a 20 gauge needle in a letter to
As stated before, several factors need to be examined in
regard to amniocentesis and its complications.
The following list includes the more significant issues:
use of ultrasound and how it is utilized.
gauge of the needle.
experience of the performer.
number of attempts to be successful.
the needle traverses the placenta.
the literature is analyzed, it becomes very clear that the use of ultrasound
and how it is utilized is very important if not the most important factor in
minimizing the risk of the procedure.
The other factors in the list are important; however, without
ultrasound, you are in essence blind.
The literature actually shows us how the use of ultrasound with
amniocentesis has changed over the years.
As previously stated, the first procedures were performed blindly
without the use of ultrasound. This was
followed by only using ultrasound to identify fetal viability and placental
location. The next step in progression
was to use ultrasound to mark a site on the abdomen where a pocket of fluid was
seen. However, studies showed that these
pockets are often transient due to fetal movement and the fullness of the
maternal bladder. It is clear based on
the literature that the best approach for amniocentesis in order to minimize
the number of attempts that are needed in order to obtain enough fluid and to
minimize the number of “bloody” taps is to perform continuous ultrasound
guidance during the procedure.
A technique that is commonly utilized
in continuous ultrasound guidance is to initially use the ultrasound transducer
to identify a pocket of fluid free of the fetus and umbilical cord and to
determine the angle of the needle insertion and approximate depth. The transducer can then be placed several
centimeters away from the insertion site at an angle that allows the performer
to observe the actual needle penetration and path into the pocket of fluid
(figure 1). This technique seems to
decrease the number of bloody taps and decrease the failure rate.
Currently, before an amniocentesis
is attempted, an ultrasound should be performed to determine fetal viability
and position, placental location, number of fetuses, and gestational age. In addition, the ultrasonographer should
determine the location of amniotic fluid pockets and look for issues that might
increase the difficulty of the procedure such as uterine fibroids, etc.
In regard to needle size, it appears
that the smaller gauge needles (size 20 or 22) have less problems than larger
bore needles such as 18 or 19 gauge needles.
In addition, the experience of the performer will decrease the failure
rate and the number of bloody taps.
A failure to obtain fluid can occur
despite the use of continuous ultrasound guidance with an experienced
performer. The more common causes for
failure are as follows:
of the membranes.
2. Isolated uterine wall contraction
(which distorts the fluid pocket or makes entry into the amniotic sac
movement that changes the shape of the fluid pocket.
changing maternal bladder size.
Membrane tenting is a frustrating situation where the
needle traverses the uterine musculature, but instead of puncturing the
membranes and entering the fluid pocket, the needle actually pushes the
membranes off the inner uterine wall.
The issue of transplacental
procedures is one of controversy.
Several authorities believe that traversing the placenta can increase
the complication rate, while others disagree.
The majority of studies do not have enough cases of transplacental
needle passage to actually make a comparison.
It does seem apparent that intra-amniotic bleeding is more common
following a transplacental procedure, however, membrane tenting is less
common. Most experienced individuals
will try to avoid the placenta if possible.
Finally, a common question is
whether an amniocentesis is more risky in patients who have a history of
pregnancy loss. Very few studies are in
existence that have analyzed this question.
Most studies outside of amniocentesis have shown that women with a
history of first trimester pregnancy loss who make it past the first trimester
have no higher complication rate when compared to women who do not have a
history of pregnancy loss. This would
suggest that the primary problem in these women is the first trimester. In that respect, most amniocentesis
procedures occur after the first trimester.
The majority of genetic amniocentesis procedures are
performed between 15 and 20 weeks of gestation.
One of the arguments against this time period is that the result is
obtained later in the pregnancy making it more difficult to act upon. Therefore, an “early amniocentesis” procedure
has been reported, which is one that is performed between 11 and 14 weeks
gestation. Several studies have looked
at the loss rate with early amniocentesis compared to routine amniocentesis and
the majority have shown only a slightly higher rate with the early
procedure. Therefore, it might be prudent
to recommend that women who have a history of first trimester pregnancy loss
wait until they go beyond the first trimester before an amniocentesis is
performed. This issue, however, is a
discussion that should occur between the patient and her healthcare
The Significance of Brown Fluid:
When a genetic amniocentesis is
performed, the amniotic fluid should be clear. Periodically, a brown or green
colored fluid is encountered. From
30,257 genetic procedures obtained from combining 16 different studies, a total
of 677 brown or green fluid samples were identified for an overall occurrence
of about 2% (range of 1% to 7%). The
pregnancy outcome was reported for 517 of these cases. A total of 62 pregnancies were lost for a
rate of 12%. This is higher than the
loss rate for pregnancies with clear fluid but not unexpected when the cause
for the discoloration is revealed.
When the pigment is analyzed, the
result is hemoglobin in over 90% of the cases.
This is consistent with the fact that in over 50% of cases in which
discolored fluid is found, a history of bleeding during the pregnancy has
occurred. Usually, the hemoglobin
content is adult suggesting it is from the mother, but occasionally it can
involve fetal hemoglobin. In addition,
if the amniotic fluid AFP is elevated in the presence of this fluid, the fetal
loss rate is even higher (again suggesting that the discoloration was fetal in
Intra-amniotic Bleeding and Potential Concerns:
In most cases, once the needle has
entered the amniotic sac and fluid is obtained, the ultrasonographer will turn
their attention to the fetus and other intrauterine contents. However, if the site where the needle
penetrates the intrauterine cavity is observed after the needle is removed,
intrauterine bleeding can be seen. One
prospective study identified intrauterine bleeding in 38% of the cases (in
which the placenta was not traversed), but the bleeding stopped in less than 30
seconds over 90% of the time. There were
no differences in pregnancy outcome when the pregnancies with bleeding were
compared to no bleeding. This would
suggest that visible bleeding is a normal occurrence with amniocentesis but is
also unavoidable. In fact, in a few
cases, the bleeding lasted for several minutes and intrauterine clots developed
(figures 2, 3 & 4). If an
ultrasonographer is unaware that this can occur, they might misinterpret these
clots as fetal malformations, masses, or amniotic bands, etc.
The fact that visible bleeding can
occur raises a concern with performing an amniocentesis on pregnant women who
have a blood borne infection that may not cross the placenta under normal
circumstances. For example, studies have
shown that the majority of newborns infected with the hepatitis B virus become
infected at the time of delivery. This
is why obstetrics tries to identify pregnant women who are carriers of this
virus and immunize the baby at delivery to potentially prevent infection. However, an amniocentesis on a hepatitis B
carrier might expose the neonate to the virus several weeks to months before
the delivery without the benefit of immunization. Unfortunately, at the present time, it is
unknown whether an amniocentesis is potentially harmful in exposing the neonate
to certain maternal blood borne infections such as hepatitis B or HIV (human
immunodeficiency virus) etc.
Amniocentesis and Rh negative women:
Several studies have been performed
that have analyzed whether an amniocentesis increases the potential for fetal
to maternal hemorrhage. To answer this
question, researchers used the Kleihauer-Betke test (an analysis of maternal
blood for the presence of fetal cells) or a rise in the maternal serum AFP
level. In short, nearly every study has
shown that fetal to maternal bleeding does occur with some amniocentesis
procedures. For the most part, these
fetal to maternal bleeds are very small and do not result in any untoward
outcome. However, in a pregnant woman
who is Rh negative (who might be carrying an Rh positive fetus), exposure to Rh
positive fetal blood could sensitize her to the Rh antigen and lead to
significant future obstetrical difficulties.
Therefore, the Rh status of pregnant women should be known prior to the
procedure and those who are Rh negative should be offered Rhogam to potentially
prevent the risk of sensitization. The
administration of anti-D immunoglobulin (Rhogam) is recommended by ACOG for
pregnant women who are Rh negative.
Amniocentesis is a common
obstetrical procedure that has a very low complication rate. It is the use of ultrasound that has primarily
reduced this rate. An amniocentesis can
be used to obtain very important information for the pregnant couple and for
healthcare personnel. However, it is
important to understand why the procedure is suggested and the couple should
have good informed consent. In addition,
the information that is to be obtained from the amniocentesis should have the
potential of affecting the course of the pregnancy.
path of the amniocentesis needle directed into the amniotic sac.
path of the amniocentesis needle through the edge of the placenta
stream of bleeding seen after the needle was removed.
4 A clot
of blood collected next to the fetal head (the baby delivered at term and was
College of Obstetricians and
Gynecologists. Prevention of Rh D
alloimmunization. Washington DC 1999 p. 1-8
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Dr. Towers is currently Professor and Vice Chair of the Department of Obstetrics & Gynecology at University of Tennessee Medical Center Knoxville in the Division of Maternal-Fetal Medicine. He is still clinically active managing numerous high-risk pregnancies. He is also actively involved in research with over 90 publications in major medical journals. Though his research has spanned many areas in obstetrics, he has primary interests in drugs in pregnancy, infections in pregnancy, fetal heart monitoring, bleeding in pregnancy, and fetal lung maturity.
He has authored a book for consumers regarding the safety of over-the-counter medications that are used in treating the common cold entitled “I’m Pregnant & I Have a Cold – Are Over-the-Counter Drugs Safe to Use?” published by RBC Press, Inc. He is also one of the new Editors of the reference book for clinical care providers entitled “Drugs in Pregnancy and Lactation, published by Wolters & Kluwer.