If you just found out you're pregnant, one of the first -
and most important - tests you should expect is a blood-type test.
This basic test determines your blood type and Rh factor. Your Rh
factor may play a role in your baby's health, so it's
important to know this information early in your pregnancy.
About the Rh Factor
People with different blood types have proteins specific to that
blood type on the surfaces of their red blood cells (RBCs). There
are four blood types - A, B, AB, and O.
Each of the four blood types is additionally classified
according to the presence of another protein on the surface of RBCs
that indicates the Rh factor. If you carry this protein, you are Rh
positive. If you don't carry the protein, you are Rh
Most people - about 85% - are Rh positive. But if a woman who is
Rh negative and a man who is Rh positive conceive a baby, there is
the potential for a baby to have a health problem. The baby growing
inside the Rh-negative mother may have Rh-positive blood, inherited
from the father. Approximately half of the children born to an
Rh-negative mother and Rh-positive father will be Rh positive.
Rh incompatibility usually isn't a problem if it's the
mother's first pregnancy because, unless there's some sort
of abnormality, the fetus's blood does not normally enter the
mother's circulatory system during the course of the
However, during delivery, the mother's and baby's blood
can intermingle. If this happens, the mother's body recognizes
the Rh protein as a foreign substance and can begin producing
antibodies (protein molecules in the immune system that recognize,
and later work to destroy, foreign substances) against the Rh
proteins introduced into her blood.
Other ways Rh-negative pregnant women can be exposed to the Rh
protein that might cause antibody production include blood
transfusions with Rh-positive blood, miscarriage, and ectopic
Rh antibodies are harmless until the mother's second or
later pregnancies. If she is ever carrying another Rh-positive
child, her Rh antibodies will recognize the Rh proteins on the
surface of the baby's blood cells as foreign, and pass into the
baby's bloodstream and attack those cells. This can lead to
swelling and rupture of the baby's RBCs. A baby's blood
count can get dangerously low when this condition, known as
of the newborn
Preventing and Treating Rh Disease of the Newborn
In generations past, Rh incompatibility was a very serious
problem. Fortunately, significant medical advances have been made
to help prevent complications from Rh incompatibility and to treat
any newborn affected by Rh disease.
Today, when a woman with the potential to develop Rh
incompatibility is pregnant, doctors administer a series of two
shots during her first pregnancy. The first shot is given around
the 28th week of pregnancy and the second within 72 hours after
giving birth. Rh immune-globulin acts like a vaccine, preventing
the mother's body from producing any potentially dangerous Rh
antibodies that can cause serious complications in the newborn or
complicate any future pregnancies.
A dose of Rh immune-globulin may also be given if a woman has a
miscarriage, an amniocentesis, or any bleeding during
If a doctor determines that a woman has already developed Rh
antibodies, then the pregnancy will be closely monitored to make
sure that those levels are not too high. In rare cases, if the
incompatibility is severe and the baby is in danger, a series of
special blood transfusions (called exchange transfusions) can be
performed either while the baby is still in the uterus or after
Exchange transfusions replace the baby's blood with RBCs
that are Rh-negative. This procedure stabilizes the baby's
level of red blood cells and minimizes further damage caused by
circulating Rh antibodies already present in the baby's
Because of the success rate of the Rh immune-globulin shots,
exchange transfusions are needed in fewer than 1% of
Rh-incompatible pregnancies in the United States today.
If Rh Disease Is Not Prevented
Rh incompatibility rarely causes complications in a first
pregnancy and does not affect the health of the mother. But Rh
antibodies that develop during subsequent pregnancies can be
potentially dangerous to mother and child. Rh disease can result in
severe anemia, jaundice, brain damage, and heart failure in a
newborn. In extreme cases, it can cause the death of the fetus
because too many RBCs have been destroyed.
If you're not sure what your Rh factor is and think
you're pregnant, it's important to start regular prenatal
care as soon as possible - including blood-type testing. With early
detection and treatment of Rh incompatibility, you can focus on
more important things - like welcoming a new, healthy baby into
Steven Dowshen, MD
Date reviewed: December 2008
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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