Topic Overview

What is Rh sensitization during pregnancy?

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

What causes Rh sensitization during pregnancy?

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.

Who gets Rh sensitization during pregnancy?

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.

How is Rh sensitization diagnosed?

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.

How is Rh sensitization prevented?

If you have Rh-negative
blood but are not Rh-sensitized, your doctor will give you one or more shots of
Rh immune globulin (such as RhoGAM). This prevents Rh sensitization in nearly all women who use it.footnote 1

You may get a shot of Rh immune globulin:

  • If you have a test such as an
  • Around week 28 of your pregnancy.
  • After delivery if your newborn is Rh-positive.

The shots only work for a short time, so you will need to repeat
this treatment each time you get pregnant. (To prevent sensitization in future
pregnancies, Rh immune globulin is also given when an Rh-negative woman has a
miscarriage, abortion, or ectopic pregnancy.)

The shots won’t work if you are already Rh-sensitized.

How is it treated?

If you are Rh-sensitized, you will have regular testing to see
how your baby is doing. You may also need to see a doctor who
specializes in high-risk pregnancies (a perinatologist).

Treatment of the baby is based on how severe the loss of red
blood cells (anemia) is.

  • If the baby’s anemia is mild, you will just
    have more testing than usual while you are pregnant. The baby may not need any
    special treatment after birth.
  • If anemia is getting worse, it may
    be safest to deliver the baby early. After delivery, some babies need a
    blood transfusion or treatment for
  • For severe anemia, a baby can have a blood transfusion
    while still in the uterus. This can help keep the baby healthy until he or she
    is mature enough to be delivered. You may have an early
    C-section, and the baby may need to have another blood
    transfusion right after birth.

In the past, Rh sensitization was often deadly for the baby. But
improved testing and treatment mean that now most babies with Rh disease
survive and do well after birth.

Frequently Asked Questions

Learning about Rh sensitization during pregnancy:

Being diagnosed:

Getting treatment:

Ongoing concerns:

Living with Rh sensitization:


Rh sensitization can occur when a person with
Rh-negative blood is exposed to Rh-positive blood.
Most women who become sensitized do so during childbirth, when their
blood mixes with the Rh-positive blood of their fetus. After being exposed, a mother’s
immune system produces
antibodies against Rh-positive red blood cells.

The minimum amount of blood mixing that causes sensitization
is not known. But many women become sensitized during pregnancy or
childbirth after being exposed to as little as 0.1 mL of Rh-positive fetal blood.footnote 1 Fortunately, Rh sensitization
can almost always be prevented with the
Rh immune globulin injection.

When an Rh-negative person’s immune system is first exposed to
Rh-positive blood, it takes several weeks to develop immunoglobulin M, or IgM,
antibodies. IgM antibodies are too large to cross the
placenta. So the Rh-positive fetus that first
triggers maternal sensitization is usually not harmed.

A previously Rh-sensitized immune system rapidly reacts to
Rh-positive blood, as during a second pregnancy with an Rh-positive fetus.
Usually within hours of Rh-positive blood exposure, smaller immunoglobulin G,
or IgG, antibodies are formed. IgG antibodies can cross the placenta and
destroy fetal red blood cells. This causes
Rh disease, which is dangerous for the fetus.

Some Rh-negative people never become sensitized, even after
exposure to large amounts of Rh-positive blood. The reason for this is not


If you are already
Rh-sensitized or become Rh-sensitized while pregnant,
you will not have any unusual symptoms.

Fetal problems from Rh sensitization are detected with
Doppler ultrasound testing and sometimes with
amniocentesis. It is possible, though, that a fetus
with severe Rh disease will move less frequently than it did earlier in the

conditions with symptoms similar to Rh sensitization
include other blood type incompatibility problems and fetal infections.

What Happens

If you are Rh-negative

Unless you are given
Rh immune globulin just before or after a high-risk event, such as
amniocentesis, abortion,
ectopic pregnancy, or childbirth, you have a chance of
becoming sensitized to an Rh-positive fetus’s blood.

If you have been Rh-sensitized in the past

If you have been Rh-sensitized in the past, you must be closely
watched during any pregnancy with an Rh-positive partner, because
your fetus is more likely to have Rh-positive blood. In response to an
Rh-positive fetus, your immune system may quickly develop IgG antibodies, which
can cross the placenta and destroy fetal red blood cells. Each subsequent
pregnancy with an Rh-positive fetus may produce more serious problems for the
fetus. The resulting fetal disease (called Rh disease,
hemolytic disease of the newborn, or erythroblastosis
fetalis) can be mild to severe.

  • Mild Rh disease involves limited destruction
    of fetal red blood cells, possibly resulting in mild fetal
    anemia. The fetus can usually be carried to term and
    requires no special treatment but may have problems with
    jaundice after birth. Mild Rh disease is more likely
    to develop in the first pregnancy after sensitization has
  • Moderate Rh disease involves the destruction of larger
    numbers of fetal red blood cells. The fetus may develop an enlarged
    liver and may become moderately anemic. The fetus may
    need to be delivered before term and may require a blood transfusion before
    (while in the uterus) or after birth. A newborn with moderate Rh disease is
    watched closely for jaundice.
  • Severe Rh disease (fetal hydrops) involves widespread destruction of
    fetal red blood cells. The fetus develops severe anemia, liver and
    spleen enlargement, increased
    bilirubin levels, and fluid retention (edema). The
    fetus may need one or more blood transfusions before birth. A fetus with severe
    Rh disease who survives the pregnancy may need a blood exchange. This procedure
    replaces most of the infant’s blood with donor blood (usually type O,
  • A history of pregnancy with Rh disease is a sign that
    you will need special treatment when you are pregnant with an Rh-positive

If you have been Rh-sensitized in the past, an Rh-negative fetus
cannot trigger an immune reaction.

What Increases Your Risk

Rh sensitization can occur when a person with
Rh-negative blood is exposed to Rh-positive blood.
During pregnancy, an Rh-negative woman can become
sensitized if she is carrying an Rh-positive

Things that increase the risk of blood mixing and sensitization
during pregnancy include:

Although rare, Rh sensitization has been known to occur after
needle sharing between intravenous drug users. Transfusing Rh-positive blood in
an Rh-negative person can also trigger sensitization. But this is
extremely rare, because blood is always tested prior to transfusion.

When To Call a Doctor

If you are already Rh-sensitized and are pregnant

Your pregnancy will be closely monitored. Discuss possible
symptoms early in pregnancy with your doctor. Repeated diagnostic
testing will be needed to watch the fetus.

Call your doctor immediately
if you note a decrease in your fetus’s movement after 24 to 26 weeks of

If you are Rh-negative

Call your doctor immediately
if you:

  • Think you may have been pregnant and
  • Are pregnant and have had an accident that may have
    injured your abdomen.

Who to see

A woman who may have problems with
Rh incompatibility or sensitization can be treated

If you test positive for Rh sensitization, your health care
system or health professional may want you to be followed and treated by a
perinatologist or an obstetrician who can easily call in a

To prepare for your appointment, see the topic Making the Most of Your Appointment.

Exams and Tests

If you are pregnant, you will have your first prenatal tests during
your first
trimester. Every woman
has her blood tested at the first prenatal visit to see what her blood type is. If your blood is
Rh-negative, it will also be tested for
antibodies to Rh-positive blood. If you have
antibodies, that means that you have been
sensitized to Rh-positive blood. The antibodies can
now kill Rh-positive red blood cells.

If you are Rh-negative and your partner is Rh-positive,
your fetus is likely to be Rh-positive.

If you are pregnant or have
miscarried, or if you have had an elective abortion, a
partial molar pregnancy, or an
ectopic pregnancy, you will need testing to see if you
have been sensitized to Rh-positive blood.

If you are Rh-negative

All pregnant women have an
indirect Coombs test during early pregnancy.

  • At the first prenatal visit, your blood is
    tested to see if you have been previously sensitized to Rh-positive blood. If
    you are Rh-negative and test results show that you are not sensitized, a repeat
    test may be done between 24 and 28 weeks.
  • If test results at 28
    weeks show that you have not been sensitized, no additional tests for
    Rh-related problems are done until delivery (barring complications such as
    placenta abruptio). You will also have a shot of Rh
    immune globulin. This lowers your chances of being sensitized during the last
    weeks of your pregnancy.
  • If your newborn is found to be
    Rh-positive, your blood will be screened again at delivery with an indirect
    Coombs test to see if you have been sensitized during late pregnancy or
    childbirth. If you have not been sensitized, you will have another shot of Rh
    immune globulin.

If you are sensitized to the Rh factor

If you are already Rh-sensitized or become sensitized while
pregnant, close monitoring is important to determine whether your fetus is
being harmed.

  • If possible, the father will be tested to see
    if the fetus could be Rh-positive. If the father is Rh-negative, the fetus is
    Rh-negative and is not in danger. If the father is Rh-positive,
    other tests may be used to learn the
    fetus’s blood type. In some medical centers, the mother’s blood can be tested
    to learn her fetus’s blood type. This is a new test that is not widely
  • An
    indirect Coombs test is done periodically during your
    pregnancy to see if your Rh-positive antibody levels are increasing. This is
    the typical course of treatment for most sensitized women during
  • Fetal
    Doppler ultrasound of blood flow in the brain shows
    fetal anemia and how bad it is. At a medical center with Doppler experts, this
    test can give you the same anemia information as
    amniocentesis, without the risks.
  • Amniocentesis may be done to check
    amniotic fluid for signs of fetal problems or to learn the fetus’s
    blood type and Rh factor.
  • Fetal blood sampling (cordocentesis) may be done to
    directly assess your fetus’s health. This procedure is used on a limited basis,
    usually for monitoring known sensitization problems (as when a mother has had
    previous fetal deaths, or when other testing has shown signs of fetal
  • Electronic fetal heart monitoring
    (nonstress test) may be done in the third trimester to check your fetus’s
    condition. Unusual fetal heart rhythms detected during a nonstress test may be
    a sign that the fetus has
    anemia related to the sensitization.
  • Fetal ultrasound testing can be used as a pregnancy
    progresses to detect sensitization problems, such as fetal fluid retention (a
    sign of severe Rh disease).

Treatment Overview

If you are sensitized to the Rh factor

If your blood is Rh-negative and you have been
sensitized to Rh-positive blood, you now have
antibodies to Rh-positive blood. The antibodies kill
Rh-positive red blood cells. If you become pregnant with an Rh-positive baby
(fetus), the antibodies can destroy your fetus’s red blood cells. This can

If you are already Rh-sensitized and are pregnant, your treatment
will focus on preventing or minimizing fetal harm and on avoiding early
(preterm) delivery.

Treatment options depend on how well or poorly the fetus is

  • If testing shows that your fetus is Rh-positive but is only
    mildly affected by your Rh factor antibodies, you will be closely watched
    until your pregnancy reaches term. Your fetus will be delivered early only if
    his or her condition gets worse.
  • If testing shows that your fetus is
    moderately affected by your Rh antibodies, your fetus’s condition will be
    closely watched until his or her lungs are mature enough for a preterm
    delivery. A
    cesarean section may be used to deliver the baby
    quickly or to avoid the difficulty of
    inducing labor before term. A moderately affected
    newborn sometimes needs a blood transfusion immediately after
  • If testing shows that your fetus is severely affected by
    your Rh factor antibodies, a
    blood transfusion may be given before birth (intrauterine fetal blood transfusion). This can be
    done through the fetus’s abdomen or directly into the fetus’s umbilical cord. A
    preterm delivery is likely to be needed. Multiple blood transfusions are
    sometimes needed to keep a fetus healthy until the fetal lungs mature enough
    to function after birth. Often a cesarean section is done to deliver the baby
    quickly. A blood transfusion is sometimes needed immediately after birth.


If you are Rh-negative and pregnant

If you are an
Rh-negative woman and you have conceived with an
Rh-negative partner, you are not at risk of
Rh sensitization during pregnancy. (Most health
professionals treat all Rh-negative pregnant women as
though the father might be Rh-positive.)

If you are already sensitized to the Rh factor, your pregnancy
will need to be closely monitored to prevent fetal harm. For more information
on fetal and newborn treatment, see Treatment Overview.

If you are unsensitized
Rh-negative, treatment focuses on preventing Rh sensitization during pregnancy
and childbirth.
Rh immune globulin (such as RhoGAM) is a highly effective treatment for
preventing sensitization.

  • To prevent sensitization from occurring late
    in the pregnancy or during delivery, you must have a shot of Rh immune globulin
    around week 28 of your pregnancy. This treatment prevents your immune system
    from making
    antibodies against your fetus’s Rh-positive red blood
  • Rh immune globulin injection is also necessary if you have
    had an obstetric procedure such as
    amniocentesis or
    external cephalic version.
  • If your newborn
    is Rh-positive, you are given Rh immune globulin again within 72 hours after
    delivery. By preventing Rh sensitization from delivery, you are protecting your
    next Rh-positive fetus.
  • If your newborn is Rh-negative, sensitization cannot happen,
    and no treatment is needed.

Rh immune globulin is also needed within 72 hours after vaginal bleeding, a
partial molar pregnancy,
ectopic pregnancy, or abortion.


Use of
Rh immune globulin is effective in preventing
Rh sensitization.footnote 1 Rh
immune globulin contains Rh
antibodies that have been purified from human donors.
This treatment prevents an unsensitized Rh-negative mother from making
antibodies against her fetus’s Rh-positive blood.

If an affected fetus younger than 34 weeks needs to be delivered,
corticosteroid medicine (betamethasone or dexamethasone) may be given to the mother to speed fetal lung
development before a premature birth.

Other Treatment

intrauterine fetal blood transfusion is sometimes used
to supply healthy blood to a fetus with severe
hemolytic disease of the newborn (also called Rh
disease or erythroblastosis fetalis).

blood transfusion or exchange transfusion is
sometimes given to a newborn to treat severe
anemia or
jaundice related to Rh disease.

Other Places To Get Help


American Congress of Obstetricians and Gynecologists



  1. American College of
    Obstetrics and Gynecology (1999, reaffirmed 2016). Prevention of Rh D alloimmunization. ACOG Practice Bulletin No. 4. International Journal of Gynaecology and Obstetrics, 66(1): 63-70. Accessed April 7, 2017.

Other Works Consulted

  • Moise KJ Jr (2008). Management of rhesus alloimmunization in pregnancy. Obstetrics and Gynecology, 112(1): 164-176.
  • Roman AS (2013). Late pregnancy complications. In AH DeCherney et al., eds., Current Diagnosis and Treatment Obstetrics & Gynecology, 11th ed., pp. 250-266. New York: McGraw-Hill.
  • U.S. Preventive Services Task Force (2004). Screening for Rh (D) incompatibility. Rockville, MD: Agency for Healthcare Research and Quality. Available online:


ByHealthwise Staff
Primary Medical Reviewer Sarah Marshall, MD – Family Medicine
Kathleen Romito, MD – Family Medicine
E. Gregory Thompson, MD – Internal Medicine
Adam Husney, MD – Family Medicine
Elizabeth T. Russo, MD – Internal Medicine
Specialist Medical Reviewer Kirtly Jones, MD – Obstetrics and Gynecology

Current as ofMay 4, 2017