Each person's blood is one of four major types: A, B, AB, or O. Blood types are determined by
the types of antigens on the blood cells. Antigens are proteins on the surface of blood cells that can cause a
response from the immune system. The Rh factor is a type of protein on the surface of red blood cells. Most
people who have the Rh factor are Rh-positive. Those who do not have the Rh factor are Rh-negative.
How do I know if I am Rh negative or Rh positive?
As part of your prenatal care, you will have blood tests to find out your blood type. If your
blood lacks the Rh antigen, it is called Rh-negative. If it has the antigen, it is called Rh-positive.
When the mother is Rh-negative and the father is Rh-positive, the fetus can inherit the Rh
factor from the father. This makes the fetus Rh-positive too. Problems can arise when the fetus's blood has the Rh
factor and the mother's blood does not.
What may happen if I am Rh-negative and pregnant?
If you are Rh-negative, you may develop antibodies to an Rh-positive baby. If a small amount of
the baby's blood mixes with your blood, which often happens, your body may respond as if it were allergic to the
baby. Your body may make antibodies to the Rh antigens in the baby's blood. This means you have become sensitized
and your antibodies can cross the placenta and attack your baby's blood. They break down the fetus's red blood
cells and produce anemia (the blood has a low number of red blood cells). This condition is called hemolytic
disease or hemolytic anemia. It can become severe enough to cause serious illness, brain damage, or even death in
the fetus or newborn.
Sensitization can occur any time the fetus's blood mixes with the mother's blood. It can occur
if an Rh-negative woman has had:
How can problems be prevented?
A blood test can provide you with your blood type and Rh factor.
Antibody screen is another blood test that can show if an Rh-negative woman has developed antibodies to
An injection or Rh immunoglobulin (RhIg), a blood product that can prevent sensitization of an
When is RhIg used?
RhIg is used during pregnancy and after delivery:
If a woman with Rh-negative blood has not been sensitized, her doctor may suggest that she receive RhIg
around the 28th week of pregnancy to prevent sensitization for the rest of pregnancy.
If the baby is born with Rh-positive blood, the mother should be given another dose of RhIg to prevent
her from making antibodies to the Rh-positive cells she may have received from their baby before and
The treatment of RhIg is only good for the pregnancy in which it is given. Each pregnancy and delivery
of an Rh-positive child requires repeat doses of RhIg.
Rh-negative women should also receive treatment after any miscarriage, ectopic pregnancy, or induced
abortion to prevent any chance of the woman developing antibodies that would attack a future
What are some other reasons RhIg may be given?
If and when an amniocentesis is done, fetal Rh-positive red blood cells could mix with a mother's
Rh-negative blood. This would cause her to produce antibodies, therefore making it necessary for RhIg
to be given.
An Rh-negative mother may receive RhIg after a birth even if she decides to have her fallopian tubes
tied and cut to prevent future pregnancies for the following reasons:
The woman may decide later to try to have the sterilization reversed.
There is a slight chance that the sterilization may fail to prevent pregnancy.
In case there is a need for a blood transfusion in the future, the treatment will prevent her
from developing antibodies.
What happens if antibodies develop?
Once a woman develops antibodies, RhIg treatment does not help. A mother who is Rh sensitized
will be checked during her pregnancy to see if the fetus is developing the condition.
The baby may be delivered on time, followed by a blood 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 in the
How common is an Rh factor negative?
More than 85% of people are Rh positive.
The Rh factor does not affect a person's general health.
Problems can occur during pregnancy when the baby's blood has the Rh factor and the mother's blood does
not, however it can be prevented in most cases with the medication called immunoglobulin (RhIg).