Just as there
are different major blood groups, such as A and B type blood,
there is also an Rh factor--a type of protein on the red blood
cells. Most people have the Rh factor and are said to be
Rh positive. Others do not have the Rh factor and are thus
Rh negative. Today, a simple lab test quickly determines
whether you are Rh positive or Rh negative.
The Rh factor
does not affect a person's general health. It can cause
problems during pregnancy, however. Now, with the use of
a special drug, these problems can almost always be prevented.
When
Does the Rh Factor Cause Problems for a Pregnancy?
The Rh factor
causes problems when an Rh-negative person's blood (without Rh factors)
comes in contact with Rh-positive blood (with Rh factor).
The person with Rh-negative blood may then become sensitized.
This means he or she produces antibodies to fight the Rh factor
as if it were a harmful substance. Sensitization can occur
if an Rh-negative woman becomes pregnant with an Rh-positive fetus.
An Rh-negative mother and an Rh-positive father can conceive an
Rh-positive child. The Rh-negative woman's body may produce
antibodies that then attack the fetal Rh-positive red blood cells.
During pregnancy,
although mother and fetus
have separate blood systems, blood from the fetus can cross the
placenta (an organ
connecting mother and fetus that brings nourishment and takes
away waste) into the mother's system. A small number of pregnant
women with Rh-negative blood who carry an Rh-positive fetus will
react to the fetal blood as a foreign substance and become sensitized
by making antibodies. These antibodies then go back to the
fetus and attack the fetal blood, breaking down the red blood
cells and producing anemia.
This condition is called hemolytic
disease. It can become severe enough to cause serious
illness, brain damage, or even death in the fetus or newborn.
Once formed,
these antibodies do not disappear. In a first pregnancy
with an Rh-positive fetus, the baby is usually delivered before
the mother's body develops significant amounts of antibodies,
although a small percentage of these pregnancies develop problems
during the last 3 months. In a second pregnancy with an
Rh-positive fetus, the antibodies are more likely to cause hemolytic
disease in the fetus. The condition usually becomes worse in later
pregnancies.
Sensitization
can also occur if an Rh-negative woman has had a previous miscarriage,
induced abortion, or ectopic
pregnancy (pregnancy in the tubes). There is also a
slight chance that a woman may develop antibodies after having
amniocentesis
done later in pregnancy. These are all cases in which fetal
blood (that might be Rh positive) could mix with maternal blood,
resulting in the production of antibodies that could complicate
a subsequent pregnancy.
back
to top
How
Is Hemolytic Disease Prevented?
Today, hemolytic
disease can for the most part be prevented if the Rh-negative
woman has not already made antibodies against the Rh factor from
an earlier pregnancy or blood transfusion. Rh immunoglobulin
(Rhogam) is a product that can safely prevent sensitization of an
Rh-negative mother. It suppresses her ability to respond to
Rh-positive red cells. With its use, sensitization can be prevented
almost all the time, although Rhogam is not helpful if the mother
is already sensitized.
A simple
blood test can tell a woman what her blood type and Rh factor
are. Another blood test, called an antibody screen, can
show if an Rh-negative woman has developed antibodies to Rh-positive
blood.
If an Rh-negative woman is given Rhogam, it is injected into a
muscle of the arm or buttocks. She will be "passively immunized."
This means that her body will not make antibodies that might otherwise
attack the red blood cells of her Rh-positive fetus.
Rhogam is
safe for a pregnant woman to use. The only known side effects
are a soreness where the drug was injected or a slight fever.
Both are temporary reactions.
back
to top
When
Is Rhogam Used?
During Pregnancy
and After Delivery
If a woman with Rh-negative blood has not been sensitized (has not
developed Rh antibodies), her health care provider may recommend
that she receive Rhogam around the 28th week of pregnancy to prevent
sensitization for the rest of the pregnancy. This takes care
of the small number of women who can become sensitized during the
last 3 months. Shortly after birth, if the child has Rh-positive
blood, the mother should be given another dose. This treatment
nearly eliminates all chances of developing antibodies to the Rh-positive
cells she may have received from her fetus before and during delivery.
No treatment is needed if the father or baby is also Rh negative.
The treatment
is good only for the pregnancy in which it is given. Protection
seems to last only about 12 weeks. Each pregnancy and delivery
of an Rh-positive child requires repeat doses of Rhogam.
Rh-negative women should also receive treatment after any miscarriage,
ectopic pregnancy,
or induced abortion. This prevents any chance of the woman
developing antibodies that would attack a future Rh-positive fetus.
Rhogam may
also be given if an Rh-negative woman has amniocentesis.
Amniocentesis is a procedure in which a small amount of amniotic
fluid (the fluid in the sac surrounding the fetus) is withdrawn
from the mother's uterus through a needle for testing. This can
help detect certain birth defects in the fetus during pregnancy.
If and when this is done, fetal Rh-positive red blood cells could
mix with a mother's Rh-negative blood, causing her to produce
antibodies; thus, Rhogam is given.
back
to top
What
Happens if Antibodies Develop?
Once a woman
develops antibodies, Rhogam treatment does not help. However,
health care providers are finding ways to save infants who get hemolytic
disease. An Rh-sensitized mother will be checked during her
pregnancy to see if the fetus
is developing the disease. In some cases of hemolytic disease,
the health care provider may recommend delivery at the normal time.
Delivery may be followed by a type of transfusion for the baby that
will replace the diseased blood cells with healthy blood.
For more severe cases, the baby may be delivered early or given
transfusions while still in the mother's womb.
Finally
. . .
Today, of all
Rh-negative women who run the risk of developing Rh sensitization,
most have received treatment to prevent them from developing antibodies
to Rh-positive blood. Hospitals are working with health care
providers and their patients to try and reach the remaining women
to prevent the 5,000 cases of hemolytic
disease that still occur each year. Safeguards can be
taken against Rh sensitization:
- All pregnant
women should have a blood test done at an early stage of pregnancy.
- If a
pregnant woman's blood group is Rh negative, knowing whether
the father is Rh positive or Rh negative will help identify
the risk of Rh sensitization.
- Rhogam,
given when needed, provides protection for women who have a
chance of developing Rh antibodies.
- For every
woman, a routine of regular health care before her baby is born
is the first step in ending the problem.
