Rh incompatibility

Definition

Rh incompatibility is a condition that develops when a pregnant woman has Rh-negative blood and the baby in her womb has Rh-positive blood.

Alternative Names

Rh-induced hemolytic disease of the newborn

Causes, incidence, and risk factors

During pregnancy, red blood cells from the fetus can get into the mother's bloodstream as she nourishes her child through the placenta.

If the mother is Rh-negative, her immune system treats the Rh-positive fetal cells as if they were a foreign substance and makes antibodies against the fetal blood cells. These anti-Rh antibodies may cross the placenta into the developing baby, where they destroy the baby's circulating red blood cells.

When red blood cells are broken down, they make bilirubin, which causes an infant to become yellow (jaundiced). The level of bilirubin in the infant's bloodstream may range from mild to dangerously high.

First-born infants are often not affected -- unless the mother has had previous miscarriages or abortions, which could have sensitized her system -- as it takes time for the mother to develop antibodies against the fetal blood. However, second children who are also Rh-positive may be harmed.

Rh incompatibility develops only when the mother is Rh-negative and the infant is Rh-positive. This problem has become uncommon in the U.S. and other places that provide good prenatal care. Special immune globulins, called RhoGAM, are now used to prevent RH incompatibility.

Symptoms

Rh incompatibility can cause symptoms ranging from very mild to deadly. In its mildest form, Rh incompatibility causes destruction of red blood cells.

Symptoms may include:

• Low muscle tone (hypotonia)
• Developmental delay
• Increased amount of amniotic fluid (polyhydramnios)
• Yellowing of the skin and whites of the eyes (jaundice)

Signs and tests

There may be:

• A positive direct Coombs test result
• Higher-than-normal levels of bilirubin in the baby's cord blood
• Signs of red blood cell destruction in the infant's blood

Treatment

Since Rh incompatibility is almost completely preventable with the use of RhoGAM, prevention remains the best treatment. Treatment of the already affected infant depends on the severity of the condition.

Mild Rh incompatibility may be treated with:

• Aggressive hydration
• Phototherapy using bilirubin lights

Expectations (prognosis)

Full recovery is expected for mild Rh incompatibility.

Complications

Possible complications include:

• Hydrops fetalis (potentially deadly fluid build up and swelling in the baby)
• Kernicterus (brain damage due to high levels of bilirubin)
• Neurological syndrome with mental deficiency, movement disorder, hearing loss, speech disorder, and seizures

Calling your health care provider

Call your health care provider if you think or know you are pregnant and have not yet seen a doctor.

Prevention

Rh incompatibility is almost completely preventable. Rh-negative mothers should be followed closely by their obstetricians during pregnancy.

Special immune globulins, called RhoGAM, are now used to prevent RH incompatibility.

If the father of the infant is Rh-positive or if his blood type cannot be confirmed, 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. However, women with Rh negative blood type must receive this injection:

• During every pregnancy
• If they have a miscarriage or abortion,
• After prenatal tests such as amniocentesis and chorionic villus biopsy
• After injury to the abdomen during a pregnancy

References

Stoll, BJ. Blood Disorders. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 103.