Rh Factor

The Rhesus factor, or Rh factor, is a certain type of protein found on the outside of red blood
cells. People are either Rh-positive (they have the protein) or Rh-negative (they don’t have
the protein). This is important when you’re Rh-negative and pregnant with a fetus who’s Rh-
positive.

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ContentsOverviewSymptoms and CausesDiagnosis and TestsManagement and
TreatmentPreventionOutlook / Prognosis
ContentsOverviewSymptoms and CausesDiagnosis and TestsManagement and
TreatmentPreventionOutlook / Prognosis

Overview

Complications can occur during pregnancy if you’re Rh negative and the fetus is Rh
positive. This is Rh incompatibility.

What is Rh factor?

Rh factor (or Rhesus factor) is a type of protein on the outside or surface of your red blood
cells. You inherit the protein, which means you get your Rh factor from your biological
parents. If you have the protein, you’re Rh-positive. If you don’t have the protein, you’re Rh-
negative. The majority of people, about 85%, are Rh-positive.

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During pregnancy, complications may occur if you’re Rh-negative and the fetus is Rh-
positive. This is called Rh factor incompatibility. Treatments are available to prevent
complications of Rh incompatibility.

Common blood types

The protein on the surface of your red blood cells determines your blood type. Each blood
type also has a positive or negative factor. The positive or negative next to the blood type is
your Rh factor. Your Rh factor doesn’t cause problems or hurt your health in any way. It only
becomes important when blood types are mixed together, like during pregnancy and
childbirth.

The most common blood types are:

 A positive.
 A negative.
 B positive.
 B negative.
 O positive.
 O negative.

Why is Rh factor important?

Your Rh factor doesn’t affect your overall health, but it’s important to know your Rh status if
you’re pregnant.

Symptoms and Causes

What causes Rh incompatibility?

Rh incompatibility occurs when a person who’s Rh-negative becomes pregnant with a fetus
with Rh-positive blood. With Rh incompatibility, your immune system reacts to this
difference (known as incompatibility) and creates antibodies. These antibodies drive an
immune system attack against the fetus’s red blood cells, which your body thinks are foreign
objects. This is called Rh sensitization. Your pregnancy care provider can prevent this from
happening by giving you a shot (injection) of immune globulin.

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During pregnancy, you don’t share blood with the fetus you’re carrying. However, a small
amount of blood from the fetus can mix with your blood during labor and delivery (either
vaginal or cesarean). It can also happen during:

 Tests like amniocentesis and chorionic villus sampling (CVS).

 Any type of vaginal bleeding during pregnancy.
 Injury or trauma to your abdomen.
 Early pregnancy complications like miscarriage or ectopic pregnancy.
 After external cephalic version (ECV), a maneuver to turn a breech baby.

When is the fetus at risk?

Complications don’t usually happen during a person’s first pregnancy. This is because it’s
unlikely that your blood will mix with the fetus’s blood until delivery, which means
antibodies won’t form until after the fetus is born. However, your provider still tests your Rh
factor even if it’s your first pregnancy.

Rh incompatibility becomes a problem if you become pregnant a second time and have
another Rh-positive fetus. In this case, your body will produce antibodies. These antibodies
put the second fetus at risk for complications. Once your body realizes the fetus is Rh-
positive, antibodies can pass into the fetus’s blood and attack its red blood cells. This is called
Rh disease. Rh disease can be life-threatening for the fetus.

Who is at risk for Rh incompatibility?

A person who’s Rh-negative is at risk for Rh incompatibility if they become pregnant with a
fetus who is Rh-positive. This chart helps determine the fetus’s risk for Rh incompatibility:

Other
Fetus’s RH
Pregnant Biological Parent Biological Risk Level
factor
Parent
Rh-positive Rh-positive Rh-positive None
Rh-negative Rh-negative Rh-negative None
Could be
Rh-positive Rh-negative None
either
Could be High. Rh immune globulin
Rh-negative Rh-positive
either (RhoGAM®) is necessary.
Pregnant Biological Parent
Rh-positive
Other Biological Parent
Rh-positive
Fetus’s RH factor
Rh-positive
Risk Level
None
Rh-negative
Other Biological Parent
Rh-negative
Fetus’s RH factor
Rh-negative
Risk Level
None
Rh-positive
Other Biological Parent
Rh-negative
Fetus’s RH factor
Could be either
Risk Level
None
Rh-negative
Other Biological Parent
Rh-positive
Fetus’s RH factor
Could be either
Risk Level
 Other
Fetus’s RH
Pregnant Biological Parent Biological Risk Level
factor
Parent
High. Rh immune globulin
(RhoGAM®) is necessary.

Diagnosis and Tests

What is the Rh factor test?

The Rh factor test is a simple blood test (called a type and screen) that every pregnant person
gets in the first trimester of pregnancy (usually at your first prenatal appointment). The Rh
factor test determines your Rh factor. This is important during pregnancy because if you’re
Rh-negative and the fetus is Rh-positive, you have a condition called Rh factor
incompatibility.

How is Rh incompatibility diagnosed?

A blood test diagnoses Rh incompatibility. If you become pregnant, your obstetrician will test
you to determine if you’re Rh-negative. If you’re Rh-positive, nothing else happens.

If you’re Rh-negative and your antibody screen is negative, your provider will give you Rh
immune globulin to prevent antibody formation. You’ll typically get this around 28 weeks of
pregnancy and then again within 72 hours of delivery if the fetus is Rh-positive. You may get
a dose in early pregnancy if your provider believes your blood has mixed with the fetus’s
blood.

Management and Treatment

How is Rh incompatibility treated?

Rh immune globulin (RhIg or RhoGAM®) is a medication that stops your body from making
Rh antibodies. It’s only helpful if your body hasn’t already made Rh antibodies. You receive
it as a shot (injection). Rh immunoglobulin shots are usually very successful in treating Rh-
incompatibility during pregnancy. Detecting Rh incompatibility early in pregnancy is the best
way to prevent serious complications.

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If your body already has Rh antibodies, the fetus is at risk for Rh disease. Since Rh immune
globulin won’t be helpful, the best treatment is close monitoring for the remainder of your
pregnancy. There’s a small chance your provider will want to deliver early, but this depends
on how severe the fetus’s Rh disease is.

What complications are associated with Rh incompatibility?

Rh incompatibility doesn’t affect the pregnant person. In a fetus, it can cause hemolytic
anemia. Hemolytic anemia destroys the fetus’s red blood cells faster than it can replace them.
The effects of Rh incompatibility can range from mild to severe. These effects may also
include:

 Jaundice.
 Liver failure.
 Heart failure.
 Stillbirth.

For mild side effects, the fetus may not need any treatment. Most fetuses recover fully if they
have a mild case of Rh disease.

For severe cases, the fetus may receive a blood transfusion. This procedure helps replace its
red blood cells. Providers can use special lights to help reduce bilirubin levels in fetuses that
have jaundice. You may need to give birth early to avoid serious complications of anemia.

Since the development of Rh immune globulin injections, Rh disease occurs infrequently.

What happens if antibodies develop?

Treatment with Rh immune globulin won’t help if an Rh-negative person has already made
antibodies. This is why it’s important to know your Rh factor and get treatment as soon as
possible.

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Prevention
Can Rh incompatibility be prevented?

Because Rh factor is genetic, it’s not possible to choose which Rh type the fetus has. The best
prevention is to find out your Rh factor.

Outlook / Prognosis
What is the outlook for a pregnant person with Rh-negative blood?

If you’re Rh-negative, getting RhIg injections after every possible contact with Rh-positive
blood between you and the fetus reduces the risk of them getting Rh disease. Rh
incompatibility doesn’t affect your health, only the fetus’s health.

Finding out if you have Rh factor incompatibility early will make it so that your provider can
give you Rhlg injections. It’s the best way to ensure the fetus stays healthy.
A note from Cleveland Clinic

Knowing your Rh status is important during pregnancy (or before) because it can prevent
potential complications. Luckily, your pregnancy care provider tests your blood to determine
if you’re Rh-positive or Rh-negative early in pregnancy. Rh factor incompatibility only
becomes an issue during pregnancy when you’re Rh-negative and the fetus is Rh-positive.
Your provider treats Rh incompatibility with an injection of Rh immunoglobulin (RhIg). Try
not to worry — your provider will keep a close eye on you and get you the treatment you
need to prevent any complications.

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