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Rh incompatibility

Also known as Rh factor, Rh sensitization, Rh disease. Blood type checked at the first visit; RhoGAM at 28 weeks and after birth.

Rh incompatibility is a blood-type mismatch between an Rh-negative pregnant person and an Rh-positive baby. If the two bloods mix, your immune system can build antibodies against the baby's Rh factor, a process called sensitization. The reassuring core is this: it causes you no symptoms, your first such pregnancy is almost always unaffected, and a simple, highly effective shot called RhoGAM prevents the whole problem. Thanks to that shot, the serious disease this once caused is now rare. This page explains why it matters and when you get it.

Know the warning signs When to call a provider
How common
About 15% are Rh-negative
Incompatibility arises only with an Rh-positive baby.
When
From the first visit on
Blood type is checked early; RhoGAM is given at 28 weeks and after birth.
Urgency
Routine
Prevented with a well-timed injection; report bleeding or trauma.
Outlook
Excellent with RhoGAM
Prevention has made Rh disease uncommon.

Understanding it

What is rh incompatibility?

The Rh factor is a protein on the surface of red blood cells. If you have it, you are Rh-positive; if you do not, you are Rh-negative. About 15% of people are Rh-negative, which is no problem in itself. It matters in pregnancy only when an Rh-negative person carries a baby who is Rh-positive, a type the baby can inherit from an Rh-positive father.

The issue is what happens if the baby's blood mixes with yours, which most often occurs at delivery but can also come with bleeding or certain procedures. Your immune system may read the baby's Rh protein as foreign and make antibodies against it. This is sensitization. It does not hurt you, and it usually does not affect the pregnancy in which it happens, because building those antibodies takes time.

The danger is to future Rh-positive pregnancies. Once you are sensitized, the antibodies stay with you, and in a later pregnancy they can cross the placenta and attack an Rh-positive baby's red blood cells. That causes hemolytic disease of the fetus and newborn, leading to anemia, jaundice, and, in severe cases, a dangerous fluid buildup called hydrops.

And prevention is remarkably effective. Rh immunoglobulin, best known as RhoGAM, stops your immune system from becoming sensitized in the first place. Given around 28 weeks, repeated within 72 hours of birth if your baby is Rh-positive, and after any event that could mix blood, it has cut the sensitization rate from about 16% to under 1%, one of modern obstetrics' clear success stories.

Symptoms

What are the symptoms?

Rh incompatibility causes no symptoms in the pregnant person and is found on a routine blood test. The effects, when they occur, are in the baby, and the signs to act on are the events that call for a RhoGAM shot.

Early signs

  • No symptoms in the pregnant person
  • Found on the routine blood type and antibody screen
  • In a newborn with hemolytic disease: jaundice, pallor, or unusual sleepiness

Emergency signs — call 911

  • If you are Rh-negative: any vaginal bleeding, a fall or blow to the belly, a miscarriage, or a procedure like amniocentesis, because you may need RhoGAM within 72 hours
  • In a known-sensitized pregnancy: a decrease in your baby's movements, which needs urgent evaluation for fetal anemia
  • In a newborn: yellowing of the skin or eyes, especially in the first day of life, or a baby who is very pale, floppy, or hard to wake

Why it matters

Risks to you and baby

No risk to you

Rh incompatibility does not make the pregnant person sick. It is entirely silent for you, which is why it is caught by a blood test rather than by symptoms.

Hemolytic disease in the baby

In a sensitized, unprevented pregnancy, antibodies can destroy an Rh-positive baby's red blood cells, causing anemia and jaundice. Severe cases can lead to hydrops, a dangerous fluid buildup, and to stillbirth.

Newborn jaundice

After birth, an affected baby can develop significant jaundice. If very high and untreated, this can cause a form of brain injury called kernicterus, which is why newborns are watched and treated with light therapy or, if needed, an exchange transfusion.

The reality today

Because RhoGAM prevents sensitization so effectively, serious Rh disease is now uncommon. Most Rh-negative pregnancies, managed routinely, have entirely healthy outcomes.

How it's found

How is it diagnosed?

A simple blood test at your first prenatal visit checks your blood type, your Rh status, and whether you already carry antibodies. If you are already sensitized, further testing follows to watch the baby.

Blood type and Rh test

Determines whether you are Rh-negative, the starting point for everything else.

Antibody screen (indirect Coombs)

Checks whether you already have anti-Rh antibodies, meaning you are already sensitized. This changes management.

Antibody titers and MCA Doppler

If you are sensitized, antibody levels are followed and a special ultrasound of the baby's middle cerebral artery detects fetal anemia, so it can be treated.

Newborn testing

After birth, a direct Coombs test and bilirubin level show whether the baby is affected and needs treatment.

Blood type and an antibody screen are done at the first prenatal visit. The screen is repeated before RhoGAM is given at 28 weeks.

Treatment

How is it managed?

For the common situation, an Rh-negative person not yet sensitized, management is simply prevention with RhoGAM. If you are already sensitized, care shifts to monitoring the baby for anemia.

Treatment paths

If you are Rh-negative and not sensitized, RhoGAM prevents the problem: a dose at about 28 weeks, another within 72 hours of delivery if your baby is Rh-positive, and a dose after anything that could mix blood. If you are already sensitized, RhoGAM no longer helps, and care focuses on monitoring your baby for anemia with antibody titers and middle cerebral artery Doppler, with a blood transfusion to the baby before birth (intrauterine transfusion) if needed.

Medication

Rho(D) immunoglobulin (RhoGAM), usually a 300 microgram dose, works by clearing Rh-positive fetal cells from your circulation before your immune system reacts to them. This is what drives the sensitization rate down from about 16% to under 1%.

Monitoring

Antibody screens track whether you have become sensitized. In a sensitized pregnancy, antibody titers and MCA Doppler follow the baby, and the newborn is watched for jaundice and anemia.

Can it recur?

Sensitization is permanent. Once your immune system has made anti-Rh antibodies, every future Rh-positive pregnancy is at risk, and the disease often worsens with each one. RhoGAM cannot reverse sensitization that has already happened, which is exactly why preventing it matters so much.

What you can do

Can it be prevented?

  • Get every RhoGAM dose

    If you are Rh-negative and not sensitized, do not miss a dose: at 28 weeks, after birth, and after any bleeding, trauma, or procedure that could mix blood. This is what prevents Rh disease.

  • Report bleeding, trauma, and procedures

    Tell your provider about any vaginal bleeding, a fall or blow to the belly, a miscarriage or ectopic pregnancy, or a procedure like amniocentesis, so a dose can be given inside the 72-hour window.

  • Know your blood type

    Knowing you are Rh-negative early lets your team plan your RhoGAM and check your antibody status, so nothing is missed.

Who is more at risk

Risk factors

Being Rh-negative with an Rh-positive baby
The essential prerequisite. If the baby's father is also Rh-negative, the baby will be Rh-negative and there is no incompatibility.
A prior sensitizing event without RhoGAM
A past pregnancy, miscarriage, or procedure where blood mixed and RhoGAM was not given can leave you sensitized.
Events that mix blood
Delivery, miscarriage, ectopic or molar pregnancy, abortion, amniocentesis or CVS, abdominal trauma, and turning a breech baby (external cephalic version) can all cause exposure.
Other blood-group antibodies
Antigens other than Rh, such as Kell, can cause similar hemolytic disease, and RhoGAM does not protect against those.

Do not wait

When to call your provider or 911

  • If you are Rh-negative, call your provider for any vaginal bleeding, a fall or blow to the belly, or a suspected miscarriage, since you may need RhoGAM within 72 hours.
  • Tell your team before any procedure such as amniocentesis or CVS, so RhoGAM can be arranged.
  • In a known-sensitized pregnancy, report any decrease in your baby's movements right away.
  • After birth, seek care if your newborn looks yellow in the first day, is very pale, or is unusually sleepy or floppy.
  • Confirm you received your RhoGAM at 28 weeks and after delivery if your baby is Rh-positive.

Talking to your team

Questions to ask your provider

  • Am I Rh-negative, and does my antibody screen show that I am already sensitized?
  • When will I receive RhoGAM, and will I need it after any events during this pregnancy?
  • Is the baby's father Rh-positive, and does that change my plan?
  • If I am sensitized, how will you monitor my baby for anemia?
  • What events during pregnancy should prompt me to call for a RhoGAM shot?
  • Will my newborn need testing or treatment after birth?

Keep reading

More on rh incompatibility

All pregnancy guides articles

Good to Know

Rh incompatibility FAQs

Common questions about rh incompatibility, answered.

What does it mean to be Rh-negative?

It means your red blood cells do not carry the Rh protein. About 15% of people are Rh-negative. On its own it is not a health problem. It only matters in pregnancy if you carry an Rh-positive baby and your blood mixes with the baby's.

Will Rh incompatibility make me sick?

No. It causes no symptoms in you at all. That is why it is found with a routine blood test rather than by how you feel, and why keeping up with your RhoGAM matters even though you feel completely fine.

Is my first baby at risk?

Usually not. Sensitization takes time to develop, so the first Rh-positive pregnancy is almost always unaffected. The risk is to future Rh-positive pregnancies, which is exactly why RhoGAM is given during and after the first one to prevent it.

What is RhoGAM and when do I get it?

RhoGAM is Rh immunoglobulin, a shot that keeps your immune system from becoming sensitized to the Rh factor. If you are Rh-negative and not sensitized, you get it at about 28 weeks, again within 72 hours after birth if your baby is Rh-positive, and after any event that could mix blood, such as bleeding, trauma, a miscarriage, or amniocentesis.

What if I already have Rh antibodies?

Then you are already sensitized, and RhoGAM can no longer help, because it works by preventing sensitization rather than reversing it. Care shifts to monitoring your baby for anemia with antibody levels and a special ultrasound, and treating the baby if needed.

Do I really need RhoGAM after a miscarriage or amniocentesis?

If you are Rh-negative, yes. These are situations where the baby's blood can mix with yours, and a well-timed shot prevents sensitization that could affect a future pregnancy. Make sure it is not overlooked.

What if the baby's father is also Rh-negative?

Then your baby will be Rh-negative too, and there is no incompatibility to worry about. Your provider may still confirm blood types, since paternity and blood type need to be certain before skipping RhoGAM.

Can other blood types cause the same problem?

Yes. Differences in other blood-group antigens, such as ABO or Kell, can also cause hemolytic disease of the newborn. RhoGAM only protects against Rh sensitization, so your antibody screen checks for these other antibodies as well.

Medically Reviewed · Updated

Reviewed by Dr. Grace Lin, MD, FACOG · OB-GYN

Obstetrician-gynecologist focused on reproductive and sexual health for women: pregnancy, BV, yeast, trichomoniasis and HPV/cervical screening. Our editorial guidelines →

6 Sources

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