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Rh Incompatibility and Isoimmunization

  • Cynthia M. Johnson, MA
Publication Type:


Rh Incompatibility and Isoimmunization

(RhD Incompatibility)


Rh factor is a protein on red blood cells. Rh incompatibility is when a mother has Rh-negative blood and her baby has Rh-positive blood. Rh isoimmunization is when the blood from the baby makes the mother's body create antibodies that can harm the baby's blood cells.


A baby's Rh status comes from the mother and father. If the mother is Rh negative and the father is Rh positive, the baby has at least a 50% chance of being Rh positive.

Rh isoimmunization can happen if the baby's Rh positive blood enters the mother's blood flow. This may happen during:

The mix in blood happens most often at the end of pregnancy. This means it is rarely a problem in a woman's first pregnancy. The mother's antibodies could affect a future pregnancy with a baby with Rh-positive blood even if the blood is not mixed.

A woman can also become sensitized to Rh-positive blood if she has a blood transfusion that is not a match.

Blood Flow to Fetus.

Placenta Functionhttp://services.epnet.com/getimage.aspx?imageiid=73677367si55551387.jpgsi55551387.jpgNULLjpgsi55551387.jpgNULL\\hgfiler01a\intellect\images\si55551387.jpgNULL64NULL2008-11-07261400Copyright © Nucleus Medical Media, Inc.

Risk Factors

The risk of Rh incompatibility is higher in an Rh-negative pregnant woman who:

  • Had a prior pregnancy with a baby that was Rh positive
  • Had a prior blood transfusion or amniocentesis
  • Did not get an Rh immunization during a prior pregnancy with an Rh-positive baby


Symptoms will only be in the baby. They can be mild to severe, such as:

  • Anemia—red blood cells are destroyed faster than they are made
  • Jaundice—a buildup of a substance in the blood that causes the skin to look yellow
  • Swelling of the body, which can lead to heart failure or breathing problems.


A woman's Rh factor is tested at routine visits. Blood tests will be done to:

  • Find out if the mother is Rh positive or Rh negative
  • Look for Rh antibodies
  • Keep track of antibody levels

An amniocentesis may also be done. It removes and tests a small amount of the fluid that surrounds the baby to find out if the baby is Rh positive.


The goal of treatment is to keep the baby healthy and lower the risk of this problem in future pregnancies.

Rh incompatibility will be treated by giving the mother Rh immune globulin to prevent Rh isoimmunization.

Not all babies will need to be treated. Those who do may need:

  • Medicine to help the body make red blood cells
  • A transfusion to replace blood cells that are being destroyed
  • To be delivered early


Rh incompatibility can be prevented with an injection of Rh immune globulin at week 28 of the pregnancy. A second injection will be given within 72 hours after delivery. The injections will block the mother's body from developing antibodies.

Women at risk may also be given these injections after a miscarriage, induced abortion, or ectopic pregnancy. These injections will protect the current pregnancy and future pregnancies.

Early and regular prenatal care can also help find and treat these problems before they happen.





  • Hemolytic disease of the fetus and newborn (HDFN). EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/hemolytic-disease-of-the-fetus-and-newborn-hdfn.
  • Rh factor blood type and pregnancy. American Pregnancy Association website. Available at: http://americanpregnancy.org/pregnancy-complications/rh-factor.
  • What are jaundice and kernicterus. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncbddd/jaundice/facts.html.


  • Elizabeth Margaret Prusak, MD
Last Updated:

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.