Alternate Names : Erythroblastosis Fetalis, Kernicterus, Hydrops Fetalis, Rh Isoimmunization
Rh incompatibility is a condition that occurs when the mother of a
fetus or newborn has Rh-negative blood type and the fetus or newborn has
Rh-positive blood. This incompatible blood reaction may cause problems in a
newborn as well as life-threatening problems for future pregnancies.
What is going on in the body?
The Rh factor, or rhesus factor, is a marker that may or may not be present on
the surface of a person's red blood cells. When a woman has the Rh component
in her blood, she is considered Rh positive. When she does not have the Rh
factor, she is considered Rh negative. When a person who has Rh-negative blood
is exposed to Rh-positive blood, that person's body does not recognize the Rh
factor and considers it something foreign. The body builds antibodies against
it as it would for any foreign substance that is introduced into the blood.
If the person who is Rh negative is ever exposed in the future to Rh-positive
blood, his or her body is armed to attack the red blood cells that have the Rh
factor. Problems may arise if a woman with Rh-negative blood conceives a baby
who has Rh-positive blood. (This may occur if the father of the baby has
Rh-positive blood.) The pregnant woman's body can become sensitive to the Rh
factor and build up "antibodies" to attack the Rh factor.
The build up of antibodies does not usually occur until after delivery of the
newborn. However, not all women develop antibodies to the Rh factor after
having one baby with Rh-positive blood. Generally, there is no effect on the
first-born child. If problems occur, they generally happen in second and later pregnancies.
Let's say a woman who is Rh negative becomes pregnant again and her unborn baby has Rh-positive blood. The Rh antibodies that the woman may have developed
during or after her first pregnancy can pass through the blood to her second
baby and attack the baby's red blood cells. This attack can cause hemolysis,
which is the destruction of red blood cells. The baby may start to produce more red blood cells in an effort to replace the ones that were destroyed.
What are the causes and risks of the disease?
Rh incompatibility occurs when a woman who has Rh-negative blood and a man who has Rh-positive blood conceive a baby who is Rh positive. There is generally no risk to the first baby, but rather to future babies who have Rh-positive blood.
Previous abortions or stillbirths of a fetus that had Rh-positive blood may present a risk to a woman who is Rh negative. This exposure to Rh-positive blood may be enough to cause her body to make antibodies to the Rh factor. Any future Rh-positive babies she may conceive may be at risk.