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| Amniocentesis, testing
of the amniotic fluid that surrounds the baby in the uterus, is a vital
tool in assessing the well-being of babies in certain women. An amniocentesis
is performed between the thirteenth and eighteenth week of pregnancy.
The purpose of the test is to count and analyze the number of chromosomes
present. Chromosomes contain the genetic material or blueprint that
makes us human and determines what we look like and how we function.
The normal number of chromosomes is 46, half from Mom and half from Dad.
Two of them are called the sex chromosomes and determine if the baby is
a boy or a girl. |
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DNA
Blueprint of Life
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| This genetic blueprint
is in the DNA of the cells. DNA is made up of two strands of linked
chemicals that twist together to form the chromosomes. |
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Amniocentesis
Procedure
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An area of skin on the mother's abdomen is cleansed using a Betadine-type
of solution. The mother's abdomen is then covered with a sterile
towel that has a hole in the center. The area of needle insertion
may or may not be anesthetized with a local anesthetic solution injected
just under the skin. |
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Under constant ultra-sound
guidance, a needle is then inserted through the mother's abdomen, through
the uterus and into the sac surrounding the baby. The needle insertion
is only uncomfortable for Mom when the needle first penetrates the skin.
After that, Mom just feels pressure as the needle is inserted further.
Once the needle reaches a safe place, a small amount of fluid (approximately
30 cc) is withdrawn. Within 24 hours this fluid will be replaced
by the baby. |
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The amniotic fluid is sent to a laboratory. There, cells in the fluid
are allowed to reproduce until about 50 to 60 are present. They are
then processed with chemicals that stop the cells from dividing at the
stage that the chromosomes are the most 'visible'. Cells are then
analyzed. Using a special stain to make the chromosomes visible,
the cells are stained. A very powerful electron microscope is then
used to photograph and count the chromosomes in at least fifty of the cells.
The photographs are used to assess the banding pattern, specific color
variations or stripes, on the chromosomes. Certain genetic diseases
will show specific abnormal patterns. |
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If there is a family history of a genetic disease caused by an enzyme presence
or absence, the cells are tested for this also. |
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Women who will be thirty-four at the time of delivery, women who are married
to men over the age of fifty, or couples who have a family history of a
genetic disease are candidates for an amnio. Your doctor Should discuss
whether you will need an amino at your first prenatal visit or at your
pre-conception visit. If he/she does not mention it and you are concerned,
you should ask. |
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