Rh Sensitization During Pregnancy - Topic Overview
If you are
Rh-negative, your red blood cells do not have a marker
called Rh factor on them. Rh-positive blood does have this marker. If your
blood mixes with Rh-positive blood, your
immune system will react to the Rh factor by making
antibodies to destroy it. This immune system response is called Rh
Rh sensitization can occur during pregnancy if you are
Rh-negative and pregnant with a developing baby (fetus) who has
Rh-positive blood. In most cases, your blood will not mix with your baby's
blood until delivery. It takes a while to make antibodies that can affect the
baby, so during your first pregnancy, the baby probably would not be
But if you get pregnant again with an Rh-positive baby, the
antibodies already in your blood could attack the baby's red blood cells. This
can cause the baby to have
jaundice, or more serious problems. This is called
Rh disease. The problems will tend to get worse with
each Rh-positive pregnancy you have.
Rh sensitization is one reason it's important to see your doctor
in the first trimester of pregnancy. It doesn't cause any warning symptoms, and
a blood test is the only way to know you have it or are at risk for it.
- If you are at risk, Rh sensitization can
almost always be prevented.
- If you are already sensitized,
treatment can help protect your baby.
Rh sensitization during pregnancy can only happen if a woman has
Rh-negative blood and only if her baby has Rh-positive blood.
- If the mother is Rh-negative and the father
is Rh-positive, there is a good chance the baby will have Rh-positive blood. Rh
sensitization can occur.
- If both parents have Rh-negative blood,
the baby will have Rh-negative blood. Since the mother's blood and the baby's
blood match, sensitization will not occur.
If you have Rh-negative blood, your doctor will probably treat
you as though the baby's blood is Rh-positive no matter what the father's blood
type is, just to be on the safe side.
All pregnant women get a blood test at their first prenatal visit
during early pregnancy. This test will show if you have Rh-negative blood and
if you are Rh-sensitized.
If you have Rh-negative blood but are not
- The blood test may be repeated between 24
and 28 weeks of pregnancy. If the test still shows that you are not sensitized,
you probably will not need another antibody test until delivery. (You might
need to have the test again if you have an amniocentesis, if your pregnancy
goes beyond 40 weeks, or if you have a problem such as
placenta abruptio, which could cause bleeding in the
- Your baby will have a blood test at birth. If the newborn
has Rh-positive blood, you will have an antibody test to see if you were
sensitized during late pregnancy or childbirth.
If you are Rh-sensitized, your doctor will
watch your pregnancy carefully. You may have:
- Regular blood tests, to check the level of
antibodies in your blood.
- Doppler ultrasound, to check blood flow to the baby's brain. This can show
anemia and how severe it is.
- Amniocentesis after 15 weeks, to
check the baby's blood type and Rh factor and to look for problems.