Rh Incompatibility and Isoimmunization
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Rh Incompatibility and Isoimmunization

(RhD Incompatibility)

En Español (Spanish Version)

Definition

One of the first tests performed at the beginning of a pregnancy is blood-type. This basic test determines your blood type and Rh factor. People with different blood types have proteins specific to that blood type on the surface of their red blood cells.

There are four blood types (A, B, AB, and O). Each of the four blood types is additionally classified according to the presence of another protein on the surface of red blood cells that indicates your Rh factor. If you carry this protein, you are Rh positive. If you don't carry the protein, you are Rh negative.

Most people, about 85%, are Rh positive. But if a woman who is Rh negative and a man who is Rh positive conceive a baby, there is the potential for incompatibility. The baby growing inside the Rh-negative mother may have Rh-positive blood, inherited from the father. Statistically, at least 50% of the children born to an Rh-negative mother and an Rh-positive father will be Rh positive.

Causes

Rh incompatibility occurs when a woman is Rh negative, but her fetus has inherited Rh-positive blood from the father. It rarely occurs in a woman's first pregnancy. She only becomes sensitized to the fetus's Rh-positive blood once she comes in contact with it. This is usually not until very late in pregnancy or during childbirth when fetal red blood cells can cross into the mother’s blood system through the placenta or its attachment site to the uterus.

This can also occur during a miscarriage , induced abortion, or ectopic pregnancy . In rare cases, it can happen during an amniocentesis or other invasive testing procedures related to pregnancy.

A woman can also become sensitized to Rh-positive blood if she receives an incompatible blood transfusion . In most cases of Rh incompatibility, there are not disease manifestations. If maternal antibodies develop against Rh-positive proteins, then these antibodies could affect a current or future fetus during pregnancy. This is called Rh isoimmunization.

Blood Flow to Fetus

Placenta Function

© 2008 Nucleus Medical Art, Inc.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. Risk factors include:

  • Being a pregnant woman with Rh-negative blood who had a prior pregnancy with a fetus that was Rh positive
  • Being a pregnant woman who had a prior blood transfusion or amniocentesis
  • Being a pregnant woman with Rh-negative blood who did not receive Rh immunization prophylaxis during a prior pregnancy with an Rh-positive fetus

Symptoms

Symptoms and complications only affect the fetus and/or newborn. They occur when standard preventive measures are not taken and can vary from mild to very serious. The mother's health is not affected.

Symptoms of the fetus or newborn baby include:

  • Anemia
  • Swelling of the body (also called hydrops fetalis), which may be associated with:
    • Heart failure
    • Respiratory problems
  • Kernicterus (a neurological syndrome), which can occurs in stages:
    • Early:
      • High bilirubin level (greater than 18 mg/cc)
      • Extreme jaundice
      • Absent startle reflex
      • Poor suck
      • Lethargy
    • Intermediate:
      • High-pitched cry
      • Arched back with neck hyperextended backwards (opisthotonos)
      • Bulging fontanel (soft spot)
      • Seizures
    • Late:
      • High-pitched hearing loss
      • Mental retardation
      • Muscle rigidity
      • Speech difficulties
      • Seizures
      • Movement disorder

Diagnosis

There aren't any physical symptoms that would allow you to detect on your own if you are Rh incompatible with any given pregnancy. If you are pregnant, it is standard procedure for your healthcare provider to order a blood test that will determine whether you are Rh positive or Rh negative. If the blood test indicates that you have developed Rh antibodies, your blood will be monitored regularly to assess the level of antibodies it contains. If the levels are high, an amniocentesis would be recommended to determine the degree of impact on the fetus.

Treatment

Since Rh incompatibility is almost completely preventable with the use of prophylactic immunization (immune globulin injection of RhoGAM), prevention remains the best treatment.

Immune Globulin Injection

You will be given an injection of Rho immune globulin at week 28 of the pregnancy. This desensitizes your blood to Rh-positive blood. You will also have another injection of immune globulin within 72 hours after delivery (or miscarriage, induced abortion, or ectopic pregnancy). The injection further desensitizes your blood for future pregnancies.

Treatment to Newborn

Treatment of a pregnancy or newborn depends on the severity of the condition.

  • Mild:
    • Aggressive hydration
    • Phototherapy using bilirubin lights
  • Hydrops fetalis:
    • Amniocentesis to determine severity
    • Intrauterine fetal transfusion
    • Early induction of labor
    • A direct transfusion of packed red blood cells (compatible with the infant's blood) and also exchange transfusion of the newborn—This is done to rid the infant's blood of the maternal antibodies that are destroying the red blood cells.
    • Control of congestive failure and fluid retention
  • Kernicterus:
    • Exchange transfusion (may require multiple exchanges)
    • Phototherapy

Outcome

Full recovery is expected for mild Rh incompatibility.

Both hydrops fetalis and kernicterus represent extreme conditions caused by the breakdown of red blood cells, called hemolysis. Both have guarded outcomes; hydrops fetalis has a high risk of mortality. Long-term problems can result from severe cases, including:

Prevention

Rh incompatibility is almost completely preventable. Rh-negative mothers should be followed closely by their obstetricians during pregnancy. If the father of the infant is Rh-positive, the mother is given a mid-term injection of RhoGAM and a second injection within a few days of delivery. These injections prevent the development of antibodies against Rh-positive blood. This effectively prevents the condition. Routine prenatal care should help identify, manage, and treat any complications of Rh incompatibility.

RESOURCES:

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

March of Dimes Birth Defects Foundation
http://www.modimes.org

CANADIAN RESOURCES:

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

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

References:

March of Dimes Birth Defects Foundation website. Available at: http://www.modimes.org .

Medline Plus website. Available at: http://www.nlm.nih.gov/medlineplus/ency/article/001600.htm#Prevention .

The Merck Manual of Medical Information—Home Edition. Simon and Schuster, Inc; 2000.

US National Library of Medicine website. Available at: http://www.nlm.nih.gov/ .



Last reviewed January 2008 by Ganson Purcell Jr., MD, FACOG, FACPE

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.


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