When a woman and her unborn baby carry different Rhesus (Rh) protein factors, their condition is called Rh incompatibility. It occurs when a woman 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, “blood type: AB+” might be written on your medical record.
Your Rh factor doesn’t directly affect your health. However, Rh factor becomes important during pregnancy. If a woman is Rh-negative and her baby is Rh-positive, then the woman’s body will approach the Rh-positive protein as a foreign object, if her immune system is exposed to it.
This means that if blood cells from your baby cross your bloodstream, which can happen during pregnancy, labor, and delivery, your immune system will make antibodies against your baby’s red blood cells.
Antibodies are parts of your body’s immune system. They destroy foreign substances.
If you have an Rh-negative blood type, you’re considered “sensitized” to positive blood types once your body has made these antibodies.
This means that your body might send these antibodies across the placenta to attack your baby’s red blood cells. Your placenta is the organ that connects you and your baby.
Rh incompatibility symptoms in your unborn baby can range from mild to life-threatening. When your antibodies attack your baby’s red blood cells, hemolytic disease can occur. This means your baby’s red blood cells are destroyed.
When your baby’s healthy red blood cells are destroyed, bilirubin will build up in their bloodstream.
Bilirubin is a chemical that’s created from the breakdown of red blood cells. Too much bilirubin is a sign that the liver, which is responsible for processing old blood cells, is having trouble.
Your baby may have one or more of the following symptoms if their bilirubin levels are high after birth:
- jaundice, a yellowing of the skin and whites of the eyes
- lethargy
- low muscle tone
These symptoms will subside after completing treatment for the Rh incompatibility.
Any woman who is Rh-negative and is having a child with someone who is Rh-positive or with an unknown Rh status is at risk for Rh incompatibility. However, given the low percentage of people with rH-negative blood types, this doesn’t happen often.
According to the Stanford Blood Center, the percentage of blood types breaks down roughly as follows:
| O+ | 37.4% |
| O– | 6.6% |
| A+ | 35.7% |
| A– | 6.3% |
| B+ | 8.5% |
| B– | 1.5% |
| AB+ | 3.4% |
| AB– | 0.6% |
It takes time for the body to develop antibodies, so firstborn children usually aren’t affected. However, if a mother became sensitized because of a miscarriage or abortion, her first live birth may be affected by Rh incompatibility.
A mother can be exposed to Rh-positive blood during certain prenatal tests or procedures. One example is amniocentesis. In this test, your doctor uses a needle to remove some of the fluid from the sac around your baby. This fluid can be tested for problems in the developing fetus.
A blood test to determine your Rh status will likely be done at your first prenatal visit with your doctor.
If you’re Rh-negative, your partner may also be tested. If your partner is also Rh-negative, you don’t have anything to worry about. If your partner is Rh-positive and you’re Rh-negative, your doctor will look for the following signs of Rh incompatibility.
A positive indirect Coombs test is a sign of Rh incompatibility. This test uses a blood sample to look for the presence of cell-destroying antibodies within the plasma of your blood.
Higher-than-normal levels of bilirubin in your infant’s blood is a sign of Rh incompatibility. In a full-term baby who is less than 24 hours old, the levels of bilirubin should be less than 6.0 milligrams per deciliter.
Signs of red blood cell destruction in your infant’s blood may indicate Rh incompatibility. This can be determined by the shape and structure of the red blood cells when examined under a microscope.
Your doctor can test your baby’s blood for the presence of maternal 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
- electrolytes, which are elements that regulate metabolism
- phototherapy
Phototherapy involves keeping your baby near fluorescent lights to help reduce the bilirubin in their blood.
These procedures may be repeated until the Rh-negative antibodies and excess bilirubin have been removed from your baby’s blood. Whether it must be repeated depends on the severity of your baby’s condition.
If you’re pregnant and your doctor determines that you’ve already developed antibodies against your baby, your pregnancy will be closely monitored.
You can prevent the effects of Rh incompatibility by getting an injection of Rh immune globulins (RhIg) during your first trimester, during a miscarriage, or while having any bleeding during your pregnancy.
This blood product contains antibodies to the Rh factor. If your baby has Rh-positive blood, you should get a second injection a few days after you give birth.
In very rare and serious cases, a series of special blood transfusions can be performed while your baby is in your uterus or after delivery.
However, the success of RhIg shots has made this treatment only necessary in less than 1 percent of cases of Rh incompatibility in the United States.
The general outlook is good in mild cases of Rh incompatibility.
Severe cases, in which the effects of Rh incompatibility aren’t prevented, can result in severe complications. These complications may include:
- brain damage to the baby, which is known as kernicterus
- fluid buildup or swelling in the baby
- trouble with mental function, movement, hearing, and speech
- seizures
- anemia
- heart failure
Death of the baby can also occur. Rh incompatibility is rarely a problem in countries with good medical care, however.
This condition is 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 plan.
If the father of your child is Rh-positive or his blood type is unknown, receiving preventive treatment with immune globulins will prevent serious effects.
