Rh incompatibility is a condition which develops when there is a difference in Rh blood type between that of the pregnant mother (Rh negative) and that of the fetus (Rh positive).

Alternative Names

Kernicterus; Rh-induced hemolytic disease of the newborn; Hydrops fetalis

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' circulating red blood cells. First-born infants are often not affected (unless the mother has had previous miscarriages/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. Hydrops fetalis and kernicterus have decreased markedly in frequency as a result of these preventive measures.

Signs and tests

Mild Rh incompatibility:

positive direct Coombs

evidence of

hemolysis in the infant's blood

elevated

cord blood bilirubin Hydrops fetalis:

severe

anemia

heart failure (

cardiac failure )

enlarged liver (

hepatomegaly )

respiratory

distress

bruising or purplish bruise-like lesions on the skin (

purpura ) Kernicterus -- Early:

high bilirubin level (greater than 18 mg/cc)

extreme

jaundice

absent Moro (startle) reflex

poor suck

lethargy

Kernicterus -- Mid:

high-pitched cry

arched back with neck hyperextended backwards (

opisthotonos )

bulging fontanel (soft spot)

seizures

Kernicterus -- Late (full neurological syndrome):

high pitched

hearing loss

mental retardation

muscle rigidity

speech difficulties

seizures

movement disorder

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:

aggressive hydratuion

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 to rid the 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

Expectations (prognosis)

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.

Complications

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 . 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.