Rh Incompatibility in Pregnancy: What It Is and How It Is Prevented

Blood type and the Rh factor

There are four major blood types — A, B, O and AB — named for substances found on the blood cells. Each type also carries a positive or negative sign, and that sign is the Rh factor, a protein. Blood cells that have the protein are Rh-positive; cells without it are Rh-negative. The Rh factor is inherited.

Most people are Rh-positive. Being Rh-negative does no harm to a person’s own health — but in pregnancy, it can affect the health of the fetus.

What Rh incompatibility is

Rh incompatibility means a pregnant person is Rh-negative and the fetus is Rh-positive.

Blood from the fetus can cross into the mother’s bloodstream, especially during childbirth. Her body then treats the fetus’s Rh-positive blood as a foreign substance and makes antibodies — proteins that can damage the fetus’s red blood cells.

Those antibodies usually cause no trouble in a first pregnancy. The danger comes later, because once formed, the antibodies stay in the body. In a later pregnancy with an Rh-positive fetus they can cross the placenta — the organ that grows in the uterus to supply the fetus with oxygen and nutrients — and attack the fetus’s red blood cells.

The result can be Rh disease, a serious condition that can cause a severe type of anemia.

Diagnosis

A health care provider orders blood tests in the first trimester, often at the first prenatal visit. They show whether the pregnant person is Rh-positive or Rh-negative, and whether their body has already made Rh antibodies.

Treatment and prevention

Injections of a medicine called Rh immune globulin during pregnancy can stop the body making Rh antibodies, heading off the problems of Rh incompatibility.

After delivery, what happens next depends on the baby:

• Baby Rh-positive: the mother needs another injection of Rh immune globulin.
• Baby Rh-negative: no further treatment is needed.

If the baby does need treatment, it may include phototherapy (light therapy) for jaundice, supplements that help the body make red blood cells, or, in severe cases, a blood transfusion.

Early prenatal care and treatment help prevent problems from Rh incompatibility.

Sources

Based on "Rh Incompatibility," MedlinePlus, National Library of Medicine; a work of the United States government in the public domain.