What is Rhesus Disease and How Does it Affect Pregnancy?

Richard Schwartz, MD
·4 min read

Most people have Rh-positive blood, meaning that they produce the "Rh factor," an inherited protein found on the surface of red blood cells. But about 15 percent of the white population and 7 percent of the African-American population lack the Rh factor. These people are Rh-negative.

The health of an Rh-negative person is not affected in any way. However, an Rh-negative woman is at risk of having a baby with rhesus disease (Rh disease) if:

  • She conceives a baby with an Rh-positive father

  • The baby inherits the father's Rh-positive blood type

Here’s what you need to know about the link between Rh factor and pregnancy, and what to do if your baby has Rh disease.

What is Rh Disease? 

Rhesus disease (Rh disease) is a condition caused by an incompatibility between the blood of a mother and that of her fetus. If the mother is Rh-negative and her baby is Rh-positive, during pregnancy (and especially during labor and delivery) some of the fetus's Rh-positive red blood cells may get into the mother's bloodstream. Since these red blood cells are foreign to the mother's system, her body will try to fight them off by producing antibodies against them—a process called "sensitization."

In a first pregnancy, there's very little danger to an Rh-positive baby, because the child is usually born before the mother produces substantial Rh antibodies. But a woman will continue to produce antibodies throughout her life—and during her second and subsequent pregnancies, maternal Rh antibodies can cross the placenta and reach the fetus. This may lead to rhesus disease, also known as Rh disease.

Rh disease destroys an unborn baby's blood cells, potentially resulting in jaundice (yellowing of the skin and eyes) and anemia. In some cases, Rh disease could cause brain damage, heart failure, and even death. The good news: doctors today can detect and treat Rh baby problems, so about 95 percent of babies with severe Rh disease survive.

How Common is Rh Disease?

While rhesus disease once affected 20,000 babies in the U.S. each year, it's fortunately rare today. Since 1968, a treatment that prevents Rh disease (injections of a blood product called Rh immunoglobulin) has dramatically reduced the number of babies born with it. Doctors are now able to manage it earlier than ever before, often even before birth

But not all Rh-negative mothers with Rh-positive babies get the treatment, and a small number of women can't be helped by the injections. As a result, some 4,000 babies still develop Rh disease each year.

Can Rh Disease Be Prevented?

A simple blood test can reveal if you have Rh-negative blood. Every woman should be tested early in pregnancy, or prior to pregnancy, to find out. To prevent Rh disease, an Rh-negative woman should receive an injection of Rh immunoglobulin (RhIG) within 72 hours of delivering an Rh-positive baby. This prevents sensitization in more than 95 percent of Rh-negative women.

However, studies show that about 2 percent of pregnant women become sensitized prior to delivery. For this reason, an RhIG injection is given around the 28th week of pregnancy as well.

The RhIG treatment must be repeated with each pregnancy, miscarriage, abortion, and blood transfusion with Rh-positive blood. You must also get the treatment after amniocentesis (a procedure in which a needle is inserted into the uterus to obtain a small sample of amniotic fluid) or another prenatal test called chorionic villus sampling (CVS).

Unfortunately, RhIG will not work for an Rh-negative woman who has already been sensitized (her body has produced antibodies to Rh-positive cells) by a prior pregnancy, miscarriage, abortion, or transfusion.

How is Rh Disease Treated?

If your unborn baby is Rh-positive, your doctor will need to measure the levels of antibodies in your blood as pregnancy progresses. If high levels of antibodies are found, tests will be given to help determine whether the baby is developing anemia (a sign of Rh disease) and if so, how severe it may be. These tests may include amniocentesis and another procedure called cordocentesis, in which the doctor, guided by ultrasound, inserts a thin needle through the mother's abdomen into the umbilical cord to take a blood sample.

Based on test results, a doctor may advise inducing labor early, before the mother's antibodies destroy too many fetal blood cells. Or he may treat the fetus with a blood transfusion, usually using cordocentesis, as early as the 18th week of pregnancy.

If the baby has jaundice after delivery, she may be given phototherapy—meaning she’ll be placed under special blue lights. If jaundice does not respond to phototherapy, or if the baby is anemic, a blood transfusion may be necessary. But some cases of Rh disease are so mild that they require no treatment.

With widespread use of RhIG, few women today need to be concerned about Rh disease. You can protect your baby by learning your Rh status and, if you are Rh-negative, following your doctor's advice.