When a mother and her unborn baby carry different Rh protein factors, their condition is called Rh incompatibility. It is specifically caused when a mother is Rh-negative and her baby is Rh-positive. The Rh factor is a specific protein found on the surface of your red blood cells.
Like your blood type, you inherit your Rh factor type from your parents. Most people are Rh-positive, but a small percentage of people are Rh-negative. This means they lack the Rh protein. A positive or negative symbol after your blood type indicates your Rh factor. For example, your blood type on your medical records might read:
Blood type: AB+ or A-
The Rh factor does not have a direct effect on your health. However, Rh factor becomes important during pregnancy. If a woman is Rh-negative and her baby is Rh-positive, then her body will determine the Rh-positive protein to be foreign.
This means that if blood cells from the baby cross into the mother’s bloodstream, which can happen during pregnancy, labor, and delivery, her immune system will make antibodies against the baby’s red blood cells. Antibodies are part of your body’s immune system that destroys foreign substances.
Once an Rh-negative mother’s body has made these antibodies, she is considered “sensitized” to her baby. This means that her body might send these antibodies across the placenta (the organ that connects mother and child) to attack the baby’s red blood cells.
Medication can help with this condition to ensure that both the mother and baby are healthy.
Any woman who is Rh-negative and having a child with a father who is Rh-positive or Rh-unknown is at risk for Rh incompatibility. According to Merck, about 13 percent of U.S. marriages have this kind of matchup. (Merck)
It takes time for the body to develop antibodies, so firstborn children are usually not affected. However, if a mother became sensitized prior to a miscarriage or abortion, her first birth may be affected by Rh incompatibility.
The symptoms can range from mild to deadly for your unborn baby. When the mother’s antibodies attack the baby’s red blood cells, hemolytic disease can occur. This means the baby’s red blood cells are being destroyed.
When the baby’s healthy red blood cells are destroyed, bilirubin will build up in his or her bloodstream. Bilirubin is a chemical that is the byproduct of the broken-down red blood cells. Too much of it is a sign that the liver, which is responsible for processing old blood cells, is having trouble.
If bilirubin levels are high after birth, your baby may have yellowing of the skin and whites of the eyes (jaundice), lethargy, and/or low muscle tone. These symptoms will subside once treatment has been completed for the Rh incompatibility.
A blood test to determine your Rh status will likely be done at your first prenatal visit with your doctor. If you are Rh-negative, your doctor will look for the following during your pregnancy and following delivery:
- the amount of amniotic fluid around the baby. Normally there is about 5 centimeters of fluid. These levels can vary depending on how far along you are in your pregnancy, however. If you have Rh incompatibility, the level of amniotic fluid will be higher than normal.
- a positive direct Coombs’ test. This test uses a blood sample to look for the presence of cell-destroying antibodies on the surface of your red blood cells.
- higher-than-normal levels of bilirubin in the infant’s blood. In a full-term baby that is fewer than 24 hours old, the levels should be less than 6.0 mg/dL (milligrams per deciliter).
- signs of red blood cell destruction in the infant’s blood. This can be indicated by the shape and structure of the red blood cells when examined under a microscope. Additionally, your doctor can test your baby’s blood for the presence of antibodies that are breaking down the red blood cells.
Treatment focuses on preventing the effects of the incompatibility. In mild cases, the baby can be treated after birth with a series of blood transfusions, hydrating fluids and electrolytes (the elements that regulate metabolism), or phototherapy. Phototherapy involves keeping the baby near fluorescent lights to help reduce the bilirubin in his or her blood. These procedures may be repeated until the Rh-negative antibodies and excess bilirubin have been removed from the baby’s blood. Whether it must be repeated depends on the severity of the infant’s condition.
If you are pregnant and your doctor determines that you have already developed antibodies against your child, your pregnancy will be closely monitored. In some cases, a series of special blood transfusions can be performed while the baby is in utero or after delivery. This is performed in less than one percent of Rh incompatible pregnancies in the United States, according to the Nemours Foundation. (KidsHealth)
The effects of Rh incompatibility can be prevented by giving the mother an injection of Rh immune globulins (RhIg) during her first trimester of pregnancy. This blood product contains antibodies to the Rh factor. If the baby has Rh-positive blood, the mother gets a second injection a few days after she gives birth.
Outlook is good in mild cases of Rh incompatibility.
In some cases it can cause:
- brain damage to the fetus
- fluid buildup or swelling in the baby
- trouble with mental function, movement, hearing, and speech
Rh incompatibility is rarely a problem in countries with good medical care.
This condition is completely preventable. If you think you may be pregnant and have an Rh-negative blood type, you should talk with your doctor to determine the best course of action. If the father of the child is Rh-positive or his blood type is unknown, receiving preventive treatment with immune globulins will prevent serious effects of the condition.
You will need to receive immune globulins during every pregnancy, if you have a miscarriage or abortion, after any prenatal tests (such as amniocentesis), or after an injury to the abdomen during pregnancy. They may also be necessary after receiving a blood transfusion with Rh-positive blood.