Rhesus sensitization during pregnancy

What is Rhesus sensitization during pregnancy?

A doctor diagnoses "Rhesus sensitization" when Rh antibodies are detected in the mother's bloodstream. Rh antibodies are protein compounds that are produced in the mother's body in response to the entry of Rh-positive fetal red blood cells (the immune system of the expectant mother perceives these red blood cells as foreign).

Causes of Rhesus Sensitization During Pregnancy

Rhesus sensitization occurs during pregnancy when the mother has a negative Rh factor in her blood and the fetus has a positive Rh factor. In most cases, the mother's blood does not mix with the fetus's blood until after birth. The antibodies that affect the fetus are formed over time and may not be present during the first pregnancy. During the next pregnancy, when the fetus is again Rh positive, the antibodies are already present in the blood and begin to attack the fetus. As a result, the fetus develops anemia, jaundice, or more serious diseases. This is called Rh disease. The condition worsens with each subsequent pregnancy when the mother and baby have different Rh factors.

During a first pregnancy, the fetus may develop Rh disease if the mother was sensitized before or during a previous pregnancy. This may also occur if:

• Miscarriage, abortion or ectopic pregnancy and you have not been given immunoglobulin to avoid sensitization.
• Severe abdominal trauma during pregnancy.
• You had amniocentesis or chorionic villus sampling during pregnancy and were not given immunoglobulin. These tests can mix blood from the mother and baby.

Sensitization is a very important factor that should be discussed with your doctor in the first trimester of pregnancy. Sensitization does not cause any alarming symptoms and can only be detected with a blood test.

• If you are at risk, Rh sensitization can almost always be prevented.
• If you are already sensitized, you need to undergo a course of treatment to protect the health of the child.

Who is at risk for sensitization during pregnancy?

Rhesus sensitization during pregnancy can only occur if the mother has a negative Rhesus factor and the child has a positive Rhesus factor.

If the mother has a negative Rh factor and the father has a positive Rh factor, there is a high probability that the child will have the same as the father. As a result, a Rh factor conflict may occur.

If both parents have Rh-negative blood, the child will have the same. In such a situation, there can be no Rh-conflict.

If you have a negative blood type, for safety reasons your doctor will prescribe a course of treatment, regardless of your father's blood type.

Diagnosis of Rh sensitization

All pregnant women have a blood test during their first prenatal visit. The results will show that the mother is Rh negative and sensitized.

If you have negative blood type but are not sensitized:

• A repeat blood test may be ordered between 24 and 28 weeks of pregnancy. If the test results confirm that you are not sensitized, you may not need to have an additional antibody test before delivery. (A repeat test may be necessary if a pregnant woman has had an amniocentesis at 40 weeks of pregnancy or if the placenta has separated and is causing uterine bleeding.)
• Your newborn will have a blood test after birth. If your baby is Rh positive, you will need to have an antibody test to find out if you were sensitised in the late third trimester of pregnancy or during labour.

If you are sensitized, your doctor will closely monitor the progress of your pregnancy, namely:

• regularly check the level of antibodies in the blood;
• perform an ultrasound Doppler examination to determine the blood flow to the child's brain, which can detect anemia and determine the extent of the disease.

Prevention of Rhesus Sensitization

If you have negative Rh blood but are not sensitized, your doctor will give you several doses of immunoglobulin. It is effective in 99 cases out of 100.

Immunoglobulin is administered:

• in case of amniocentesis performed on a pregnant woman;
• at 28 weeks of pregnancy;
• after birth, if the child has a positive Rh blood type.

The drug only helps for a certain period of time, so a course of treatment should be taken with each pregnancy. (To avoid sensitization during repeated pregnancies, immunoglobulin is administered to women with negative Rh blood in the event of a miscarriage, abortion or ectopic pregnancy).

Injections will not be helpful if you are already sensitized.

Treatment

If you are sensitized, your doctor will conduct regular testing during pregnancy to determine the health of the fetus. You should also visit a perinatologist.

The child's course of treatment depends on the severity of the anemia.

• If you have mild anemia, you will need to have additional tests during pregnancy.
• If the condition worsens, the only correct solution is to extract the baby early. After birth, some newborns may need a blood transfusion or treatment for jaundice.
• In severe cases of anemia, the baby is given a blood transfusion in the womb. This will help protect its health and give it extra time to fully mature. In most such cases, a cesarean section is performed during labor and an additional blood transfusion is given immediately after delivery.

In the past, sensitization often resulted in the death of the child. But modern testing and treatment allow such children to be born safely and develop normally.

Causes of Rhesus Sensitization During Pregnancy

Rhesus sensitization occurs when a woman with a negative Rh factor is exposed to a positive Rh factor. About 90% of women in labor become sensitized during labor because their blood mixes with the baby's blood. Later, the woman's immune system begins producing antibodies against the Rh-positive red blood cells.

Experts do not know how much blood causes sensitization during labor. But many women become sensitized during pregnancy or labor if even 0.1 ml of Rh-positive fetal blood enters their bloodstream. Fortunately, Rh-conflict can be avoided by injecting the mother with immunoglobulin.

When a woman's immune system is first sensitized, it takes several weeks for IgM or antibodies to be produced. The antibodies are too large to cross the placenta, so no harm is done to the Rh-positive fetus. The previously sensitized immune system quickly reacts to Rh-positive blood, just as it does during a second pregnancy with an Rh-positive fetus. Usually, within a few hours of exposure to Rh-positive blood, IgG is produced. These antibodies cross the placenta to the fetus and destroy its red blood cells. A Rh-conflict occurs, which is dangerous for the unborn child.

Some Rh-negative people never become sensitized even when exposed to large amounts of Rh-positive blood. The reason for this is not yet known.

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