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Rh Sensitization and Pregnancy
Your Blood Type
|Red blood cells (RBCs) are especially important to the body
because they carry oxygen from the lungs to the rest of the body,
and remove carbon dioxide waste. On the surface of each RBC is a set
of proteins. Which proteins you have is determined genetically.
When doctors talk about these proteins, they refer to them as
your "blood type." Everyone has a blood type. One familiar set of
proteins used in blood typing refers to the A, B, O system. Your
blood type may be A, B, AB, or O.
A second familiar blood
typing system describes the presence or absence of Rh protein. (It's
called "Rh" because it was first noticed in Rhesus monkeys.) If you
have the Rh protein, you are Rh-positive. If you don't have it, you
are Rh-negative. Everyone is either Rh-positive or Rh-negative.
Your Immune System
|Your immune system functions to protect your body from
infection. In order to do that, it must be able to tell when
something doesn't belong in your body, then get rid of it. The
immune system uses a complex system to identify what is "self" (or
what's supposed to be there) and what is "nonself" (or what is
foreign and probably dangerous). Anything that the immune system
identifies as foreign is called an antigen. To protect the body, the
immune system marks all antigens to be destroyed.
immune system detects an antigen, it produces an antibody specific
to that antigen. Antibodies circulate in your blood and destroy
antigens. After the initial exposure, they can quickly recognize
their specific antigen and react to have it destroyed if it
reappears. Antibodies speed up the immune system's response to
infection. Vaccines work on this principle that the immune system
produces antibodies in response to a small exposure to an antigen.
Your Immune System and Your Blood Type
|In the blood, your immune system uses the proteins on the
surface of the RBCs to identify the cells that belong in your body.
That's why your blood type is important during transfusions, because
the immune system will destroy any blood that you receive that it
doesn't recognize. An incompatible blood transfusion can result in
severe illness and even death. If you receive a transfusion of
compatible blood, your immune system can't tell the difference
between the blood you received and the blood your body produced.
|Exposure to an incompatible blood type causes the body to
produce antibodies. When an Rh-negative person is exposed to
Rh-positive blood, his or her body produces antibodies to the Rh
factor in the blood. This reaction is called "Rh sensitization." It
is important for Rh-negative women because it affects pregnancy.
Hemolytic Disease of the Newborn
|During pregnancy, the mother's antibodies cross the placental
barrier and enter the blood of the fetus. If the mother is
Rh-negative and has been Rh-sensitized through exposure to
Rh-positive blood, she has antibodies to the Rh factor. If her baby
is Rh-positive, the mother's antibodies attack the fetus' RBCs, and
the baby is born with a disease called "hemolytic disease of the
newborn" (or HDN), or erythroblastosis fatalis.
of HDN result from a low RBC count. With fewer RBCs, the infant's
blood has a lowered ability to carry oxygen to the body. The
newborn's body tries to compensate for its anemic condition and
tries to produce a large number of RBCs in a short amount of time,
creating other problems in the body, especially the liver. The liver
becomes overworked in trying to keep up with the production of new
RBCs and the cleaning away of the dead blood cells. It becomes
enlarged and unable to keep up. The dead blood cells form bilirubin
and result in jaundice. Fluid also begins to accumulate in the
stomach, lungs, and around the heart, giving the baby a swollen
look. HDN may be fatal in the most severe cases. All of these
symptoms are a direct result of the mother's antibodies attacking
the infant's red blood cells.
|Preventing Rh sensitization, and thus preventing HDN, is a part
of routine prenatal care. Sensitization can be prevented by giving
the Rh-negative woman an injection of Rh Immune Globulin (RhIg),
such as Rhophylac, at the twenty-eighth week of pregnancy and
another 72-hours after delivery. An RhIg preparation is also given
after any possible exposure to Rh-positive blood.
to Rh-positive blood can occur not only through incompatible
transfusions, but also through carrying an Rh-positive baby. Blood
may mix in the course of pregnancy during delivery, miscarriage,
abortion, Ectopic (or tubal) pregnancy, amniocentesis, abdominal
trauma, external manipulation of the uterus such as trying to turn a
breech baby, or even across the placenta. In any pregnancy in which
an Rh-negative woman carries an Rh-positive baby, there is a risk of
Rh exposure and sensitization. If the father is known to be
Rh-negative, there is no danger of HDN or Rh sensitization because
the fetus will also be Rh-negative.
There is little risk of a
woman becoming Rh-sensitized and then affecting her fetus during her
first pregnancy. RhIg injections are given after each delivery to
protect future pregnancies. The RhIg works to clear away any
antigenic cells that may have entered the mother's body, preventing
Standard prenatal care involves the
testing of a woman's blood for Rh antibodies. If she is found to be
Rh-sensitized already, no RhIg will be administered because it will
not have any effect. Upon delivery, the baby will be watched closely
for symptoms of HDN and will be treated accordingly.