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Rh Incompatibility and Isoimmunization

(RhD Incompatibility)

Definition

Rh factor is a protein that may be found on the surface of red blood cells. If you carry this protein, your blood is Rh positive. If you don't carry this protein, your blood is Rh negative.
Sometimes a mother with Rh-negative blood is pregnant with a baby that has Rh-positive blood. This can cause a problem if the baby's blood enters the mother's blood flow. The Rh-positive blood from the baby will make the mother's body create antibodies. This is called isoimmunization. The antibodies will attack any Rh-positive blood cells. This will not cause a problem for the mother. However, the antibodies can pass to the developing baby and destroy some of the baby's blood cells.
Fortunately, Rh incompatibility is often prevented with standard prenatal care. If the condition is not prevented, the baby may need care.

Causes

A baby's Rh status is determined from the mother and father. If the mother is Rh negative and the father is Rh positive, the baby has a 50% chance of being Rh positive. However, Rh isoimmunization will only happen if the baby's Rh-positive blood enters the mother's blood flow. In most pregnancies, the mother's and baby's blood will not mix. The baby's blood may come into contact with the mother's blood flow 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 receives an incompatible blood transfusion .
Blood Flow to Fetus
Placenta Function
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Risk Factors

Factors that put you at risk for Rh incompatibility include being 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 receive Rh immunization prophylaxis during a prior pregnancy with an Rh-positive baby
At least 50% of the children born to an Rh-negative mother and an Rh-positive father will be Rh positive.

Symptoms

Symptoms and complications will only affect the baby. The complications occur when standard preventive measures are not taken. The symptoms can vary from mild to severe.
Symptoms that can develop in the baby include:
  • Anemia —low levels of red blood cells
  • Swelling of the body which may be associated with:
    • Heart failure
    • Respiratory problems
  • Symptoms of kernicterus (a syndrome of the nerves), which can occur in stages:
    • Early:
      • High bilirubin level
      • Extreme jaundice
      • Absent startle reflex
      • Poor suck
      • Lethargy
    • Intermediate:
      • High-pitched cry
      • Arched back with neck hyperextended backwards
      • Bulging soft spot on the head
      • Seizures
    • Late:
      • Loss of high-pitched hearing
      • Intellectual disability
      • Muscle rigidity
      • Speech difficulties
      • Seizures
      • Movement disorder

Diagnosis

You cannot detect Rh incompatibility on your own. It does not have any physical symptoms. A blood test can determine whether you are Rh positive or Rh negative. The blood test will also look for Rh antibodies or monitor the levels of antibodies through pregnancy. If the antibody levels are high, an amniocentesis can determine if the fetus is ill.
It is very important to have a blood test at the beginning of pregnancy.

Treatment

Rh incompatibility is almost completely preventable using prophylactic immunization. The best treatment is prevention.
If Rh incompatibility does occur the baby may need treatment based on their symptoms such as:

Mild Symptoms

Full recovery is expected for mild Rh incompatibility. Treatment may include:

Swelling of the Body (called Hydrops fetalis)

More severe condition that may require:
  • Intrauterine fetal transfusion—to replace blood cells that are being destroyed during pregnancy
  • Early induction of labor
  • A direct transfusion of packed red blood cells (compatible with the infant's blood)
  • An exchange transfusion to remove the mother's antibodies
  • Control of congestive heart failure and fluid retention

Kernicterus may be treated with:

  • Exchange transfusion—replacing baby's blood with blood with Rh-negative blood cells
  • Phototherapy
Both hydrops fetalis and kernicterus are more severe conditions. These conditions have guarded outcomes. Hydrops fetalis has a high risk of mortality. Long-term problems can also develop with severe cases, including:

Prevention

If a mother is at risk for Rh incompatibility an injection of Rho immune globulin will be given at week 28 of the pregnancy. A second injection will be given within 72 hours after delivery. These 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.
Routine prenatal care should help identify, manage, and treat any complications of Rh incompatibility.

RESOURCES

American Congress of Obstetricians and Gynecologists http://www.acog.org

American Pregnancy Association http://www.americanpregnancy.org

CANADIAN RESOURCES

Society of Obstetricians and Gynaecologists of Canada http://www.sogc.org

Women's Health Matters http://www.womenshealthmatters.ca

References

Berkow R, Beers MH, et al. The Merck Manual of Medical Information—Home Edition. New York, NY: Simon and Schuster, Inc; 2000.

Rh factor. American Pregnancy Association website. Available at: http://americanpregnancy.org/pregnancycomplications/rhfactor-2.html . Updated April 2006. Accessed October 4, 2012.

Hemolytic disease of the newborn. EBSCO DynaMed website. Available at: https://dynamed.ebscohost.com/about/about-us . Updated May 17, 2012. Accessed October 4, 2012.

Revision Information

  • Reviewer: Andrea Chisholm
  • Review Date: 03/2013 -
  • Update Date: 00/31/2013 -

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.

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