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McKesson Clinical Reference Systems: Women's Health Advisor 2002.2
Rh Incompatibility
What is Rh incompatibility?
If you are a mother with Rh incompatibility, there is a
substance in your baby's red blood cells that is not in your
blood cells. This substance is usually called the Rho(D)
factor. The baby is Rh positive and you are Rh negative.
Some of the baby's red blood cells may come in contact with
your blood. Your body may then produce antibodies to the
Rho(D) factor. This is called sensitization. The
antibodies may cross the placenta and destroy the red blood
cells in your baby or in the next Rh-positive baby you have.
This destruction of red blood cells is called hemolytic
disease.
How does it occur?
Rh incompatibility occurs only if you are Rh negative and
your baby is Rh positive. It does not occur if you are Rh
positive and your baby is Rh negative or if you both of you
are negative or positive.
Usually you are not exposed to a baby's blood until you give
birth. This usually means that your first baby is not
affected by the incompatibility. However, large amounts of
the baby's blood often leak into the mother during delivery.
Your body might then make antibodies. This can cause
problems if you have another Rh-positive baby.
Sometimes the baby's blood may come in contact with your
blood before delivery. This might happen:
- after amniocentesis or other similar tests
- during a miscarriage or abortion
- during an ectopic (tubal) pregnancy
- if you bleed heavily during pregnancy
- after a procedure used to try to change a baby's position
in the womb before birth (external cephalic version)
- if your abdomen is injured.
If you are Rh negative and you received Rh-positive blood in
a transfusion, you may have developed antibodies that will
cause Rh incompatibility.
In most cases, development of antibodies can be prevented.
What are the symptoms?
You will have no symptoms. The baby will have symptoms if
he or she develops hemolytic disease. The baby's red blood
cells will start to break down, causing anemia. The anemia
may cause other problems, such as jaundice and breathing
problems. The baby might die in the womb if too much of the
baby's blood is destroyed by the antibodies.
How is it diagnosed?
If blood tests show that you are Rh negative and have
antibodies against the Rho(D) factor, Rh incompatibility may
be a problem. If you are Rh negative, your baby's father
should be tested. If the father's blood is Rh positive, the
baby may inherit Rh-positive blood from him. If both you
and the father are Rh negative, there will not be a problem
because the baby will also be Rh negative.
Some of the tests used to check for hemolytic disease and
its effects on the baby before and after birth are:
- amniocentesis
- cordocentesis (removing blood from the baby's umbilical
cord)
- ultrasound scan
- nonstress tests
- blood tests
- biophysical profile.
How is it treated?
If you have already been sensitized by a previous birth,
your baby may have hemolytic disease before birth. If this
happens, your baby may need a blood transfusion in the womb
before birth. Sometimes early delivery by cesarean section
is necessary.
If you have not been sensitized, you will have a shot of
Rh-immune globulin (RhoGAM) at about 28 weeks of pregnancy.
You may also be given a shot within 72 hours after a birth
(if the baby is Rh positive), miscarriage, abortion, tubal
(ectopic) pregnancy, or amniocentesis. RhoGAM contains
antibodies to the Rho(D) factor. The antibodies in the
shot will destroy any red blood cells from the baby that
are in your blood. Your body will not make its own
antibodies to the Rho(D) factor. If you have the shot at 28
weeks and after delivery, sensitization will be prevented
and Rh incompatibility should not be a problem during your
next pregnancy.
It is important to have the RhoGAM shot in all cases when
the baby's blood could leak into your system. This
includes:
- during or after all pregnancies, including ectopic
pregnancies
- after early miscarriages
- after chorionic villus sampling
- after amniocentesis
- after postpartum tubal ligation
- after external cephalic version
- after injury to your abdomen.
If you have a threatened miscarriage but don't actually
miscarry, you may also need a RhoGAM shot. Discuss this
with your health care provider.
How long will the effects last?
Sensitization usually doesn't happen until after the birth
of an Rh-positive baby. Therefore, in most cases Rh
incompatibility is not a problem during your first pregnancy
and delivery of an Rh-positive baby. However, later
pregnancies and deliveries might be affected unless you are
treated with RhoGAM to prevent sensitization after EVERY
birth, miscarriage, abortion, and tubal pregnancy.
Once you become sensitized, RhoGAM is not helpful. You will
stay sensitized, and the effects are usually worse with each
pregnancy.
What can be done to help prevent the problems of Rh
incompatibility?
This problem of pregnancy has not occurred often since the
discovery of RhoGAM. RhoGAM can prevent sensitization. It
is given to Rh-negative women right after every delivery,
miscarriage, or abortion. It is also given to pregnant
Rh-negative women after amniocentesis, after any bleeding
episodes, and during the seventh month of pregnancy.
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