Rh incompatibility is a condition which develops when a pregnant woman has an Rh-negative blood type and the fetus she carries has Rh-positive blood type.
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 system cannot tolerate the presence of Rh-positive red blood cells.
In such cases, the mother's 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 fetus, where they destroy the fetus's circulating red blood cells.
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 can cause symptoms ranging from very mild to fatal. In its mildest form, Rh incompatibility causes hemolysis (destruction of the red blood cells) with the release of free hemoglobin into the infant's circulation.
Hemoglobin is converted into bilirubin, which causes an infant to become yellow (jaundiced). The jaundice of Rh incompatibility, measured by the level of bilirubin in the infant's bloodstream, may range from mild to dangerously high levels of bilirubin.
Hydrops fetalis is a complication of a severe form of Rh incompatibility in which massive fetal red blood cell destruction (a result of the Rh incompatibility) causes a severe anemia resulting in fetal heart failure, total body swelling, respiratory distress (if the infant has been delivered), and circulatory collapse. Hydrops fetalis often results in death of the infant shortly before or after delivery.
Kernicterus is a neurological syndrome caused by deposition of bilirubin into the brain (CNS) tissues. Kernicterus develops in extremely jaundiced infants, especially those with severe Rh incompatibility.
It occurs several days after delivery and is characterized initially by loss of the Moro (startle) reflex, poor feeding, and decreased activity. Later, a high-pitched shrill cry may develop along with unusual posturing, a bulging fontanel, and seizures. Infants may die suddenly of kernicterus.
If they survive, they will usually later develop decreased muscle tone, movement disorders, high-pitched hearing loss, seizures, and decreased mental ability.
Rh incompatibility develops only when the mother is Rh-negative and the infant is Rh-positive. Special immune globulins, called RhoGAM, are now used to prevent this sensitization. In developed countries such as the US, hydrops fetalis and kernicterus have decreased markedly in frequency as a result of these preventive measures.
Polyhydramnios (before birth)
Slowly or rapidly increasing jaundice
Signs and tests
Mild Rh incompatibility:
Positive direct Coombs
Evidence of hemolysis in the infant's blood
Elevated cord blood bilirubin
Heart failure (cardiac failure)
Enlarged liver (hepatomegaly)
Bruising or purplish bruise-like lesions on the skin (purpura)
Kernicterus -- Early:
High bilirubin level (greater than 18 mg/cc)
Absent Moro (startle) reflex
Poor breast-feeding or sucking
Kernicterus -- Mid:
Arched back with neck hyperextended backwards (opisthotonos)
Bulging fontanel (soft spot)
Kernicterus -- Late (full neurological syndrome):
High-frequency hearing loss
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.
Phototherapy using bilirubin lights
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 to rid the blood of the maternal antibodies that are destroying the red blood cells
Control of congestive failure and fluid retention
Exchange transfusion (may require multiple exchanges)
Full recovery is expected for mild Rh incompatibility. Both hydrops fetalis and kernicterus represent extreme conditions caused by hemolysis. Both have guarded outcomes. Hydrops fetalis has a high mortality rate.
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.
Update Date: 8/18/2006
URL of this page: http://www.nlm.nih.gov/medlineplus/ency/article/001600.htm