23 November 2008

Amniocentesis


The invention:

A technique for removing amniotic fluid from
pregnant women, amniocentesis became a life-saving tool for diagnosing
fetal maturity, health, and genetic defects.

The people behind the invention:

Douglas Bevis, an English physician
Aubrey Milunsky (1936- ), an American pediatrician




How Babies Grow

For thousands of years, the inability to see or touch a fetus in the
uterus was a staggering problem in obstetric care and in the diagnosis
of the future mental and physical health of human offspring. A
beginning to the solution of this problem occurred on February 23,
1952, when The Lancet published a study called “The Antenatal Prediction
of a Hemolytic Disease of the Newborn.” This study, carried
out by physician Douglas Bevis, described the use of amniocentesis
to assess the risk factors found in the fetuses of Rh-negative women
impregnated by Rh-positive men. The article is viewed by many as a
landmark in medicine that led to the wide use of amniocentesis as a
tool for diagnosing fetal maturity, fetal health, and fetal genetic
deects.
At the beginning of a human pregnancy (conception) an egg and
a sperm unite to produce the fertilized egg that will become a new
human being. After conception, the fertilized egg passes from the
oviduct into the uterus, while dividing and becoming an organized
cluster of cells capable of carrying out different tasks in the ninemonth-
long series of events leading up to birth.
About a week after conception, the cluster of cells, now a “vesicle”
(a fluid-filled sac containing the new human cells), attaches
to the uterine lining, penetrates it, and becomes intimately intertwined
with uterine tissues. In time, the merger between the vesicle
and the uterus results in formation of a placenta that connects the
mother and the embryo, and an amniotic sac filled with the amniotic
fluid in which the embryo floats.
Eight weeks after conception,the embryo (now afetus) is about 2.5 centimeters
long and possessesall the anatomic elements it will have when it is born.
At this time, about two and one-half months after her last menstruation,
the expectant mother typically visits a physician and finds out she is pregnant.
Also at this time, expecting mothers often begin to worry about possible birth
defects in the babies they carry.
Diabetic mothers and mothers older than thirtyfive years have higher than usual
chances of delivering babies who have birth defects.
 Many other factors inferred from the medical history an expecting
mother provides to her physician can indicate the possible appearance
of birth defects. In some cases, knowledge of possible
physical problems in a fetus may allow their treatment in the uterus
and save the newborn from problems that could persist throughout
life or lead to death in early childhood. Information is obtained
through the examination of the amniotic fluid in which the fetus is
suspended throughout pregnancy. The process of obtaining this
fluid is called “amniocentesis.”


 Diagnosing Diseases Before Birth

Amniocentesis is carried out in several steps. First, the placenta
and the fetus are located by the use of ultrasound techniques. Next,
the expecting mother may be given a local anesthetic; a long needle
is then inserted carefully into the amniotic sac. As soon as amniotic
fluid is seen, a small sample (about four teaspoons) is drawn into a
hypodermic syringe and the syringe is removed. Amniocentesis is
 nearly painless, and most patients feel only a little abdominal pressure
during the procedure.
The amniotic fluid of early pregnancy resembles blood serum.
As pregnancy continues, its content of substances from fetal urine
and other fetal secretions increases. The fluid also contains fetal cells
from skin and from the gastrointestinal, reproductive, and respiratory
tracts. Therefore, it is of great diagnostic use. Immediately after
the fluid is removed from the fetus, the fetal cells are separated out.
Then, the cells are used for genetic analysis and the amniotic fluid is
examined by means of various biochemical techniques.
One important use of the amniotic fluid from amniocentesis is
the determination of its lecithin and sphingomyelin content. Lecithins
and sphingomyelins are two types of body lipids (fatty molecules)
that are useful diagnostic tools. Lecithins are important because
they are essential components of the so-called pulmonary
surfactant of mature lungs. The pulmonary surfactant acts at lung
surfaces to prevent the collapse of the lung air sacs (alveoli) when a
person exhales.
 Subnormal lecithin production in a fetus indicates that it most
likely will exhibit respiratory distress syndrome or a disease called
“hyaline membrane disease” after birth. Both diseases can be fatal,
so it is valuable to determine whether fetal lecithin levels are adequate
for appropriate lung function in the newborn baby. This is
particularly important in fetuses being carried by diabetic mothers,
who frequently produce newborns with such problems. Often, when
the risk of respiratory distress syndrome is identified through amniocentesis,
the fetus in question is injected with hormones that help it
produce mature lungs. This effect is then confirmed by the repeated
use of amniocentesis. Many other problems can also be identified by
the use of amniocentesis and corrected before the baby is born.


Consequences

In the years that have followed Bevis’s original observation, many
improvements in the methodology of amniocentesis and in the techniques
used in gathering and analyzing the genetic and biochemical
information obtained have led to good results. Hundreds of debilitating
hereditary diseases can be diagnosed and some ameliorated—by
 the examination of amniotic fluid and fetal cells isolated by amniocentesis.
For many parents who have had a child afflicted by some hereditary
disease, the use of the technique has become a major consideration
in family planning. Furthermore, many physicians recommend strongly
that all mothers over the age of thirty-four be tested by amniocentesis
to assist in the diagnosis of Down syndrome, a congenital but nonhereditary
form of mental deficiency.
There remains the question of whether such solutions are morally
appropriate, but parents—and society—now have a choice resulting
from the techniques that have developed since Bevis’s 1952
observation. It is also hoped that these techniques will lead to
means for correcting and preventing diseases and preclude the need
for considering the therapeutic termination of any pregnancy.


See also :  Abortion pill ; Birth control pill ; CAT scanner ; Electrocardiogram ; Electroencephalogram ; Mammography ; Nuclear magnetic resonance ; Pap testAmniocentesis


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