How Your Rh Factor Can Affect Your Pregnancy

Lab technician with blood samples and medical chart.
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Babies born to women with a negative blood type are at risk of anemia and more serious hemolytic disease due to Rh factor. Fortunately, maternal screening and preventive treatment during pregnancy are routine practices in the United States.

How Blood Type Impacts Pregnancy

Your blood type is made of two parts: the blood-type group—A, B, O, AB—and the Rh factor. Rh factor is a protein in the blood. When present, a persons blood type is positive (such as A+ or O+). When the Rh protein is absent, the blood type is negative (such as AB- or B-).

Most people are Rh positive and, in general, Rh factor does not impact your life unless you need blood or are pregnant.

The problem occurs when the mother has a negative Rh factor and the father has a positive Rh factor. This combination can produce a child who is Rh positive and at risk for hemolytic disease.

When Rh Factor May Negatively Affect a Pregnancy

While the mother's and baby's blood systems are separate there are times when the blood from the baby can enter into the mother's system. This can cause the mother to create antibodies against the Rh factor, thus treating an Rh-positive baby like an intruder in her body. When this happens, the mother is considered sensitized.

A sensitized mother's body will make antibodies, which can attack an Rh-positive baby's blood. These antibodies can break down the baby's red blood cells leading to anemia. In severe cases, this hemolytic disease can cause illness, brain damage, and even death.

Sensitization can also occur during a blood transfusion, miscarriage, abortion, ectopic pregnancy, and certain procedures like amniocentesis.

The antibodies rarely cause a problem in first pregnancies, but they do not disappear, and it is very important to be screened and give an accurate medical history to your doctor or midwife.

How Hemolytic Disease Is Prevented

Hemolytic disease can be prevented in women who are not already sensitized. Rho(D) immune globulin (brand name Rhogam) is a blood product given by injection to help the Rh negative mother by minimizing her reaction to the Rh-positive red cells.

Reactions to this medication are generally minor, including soreness at the injection site and sometimes a slight fever.

Since a small number of unsensitized women may have problems with the end of pregnancy, many practitioners recommend that she be given a Rhogam injection at 28 weeks gestation to prevent the few cases of sensitization that occur at the end of pregnancy.

One dose of Rhogam lasts about 12 weeks. An Rh-negative mother will also be given Rhogam within 72 hours of birth if the child is Rh positive. The baby's blood type can be determined easily after birth by cord blood samples.​​​

Rhogam may also be given after an amniocentesis, miscarriage, abortion, or postpartum sterilization (tubal ligation). This is because there is a small chance of blood contamination and potential sensitization even after these procedures or occurrences.

What Happens If Hemolytic Disease Is Diagnosed

There are about 5,000 cases of hemolytic disease that will occur each year. A mother who is Rh sensitized will be screened throughout her pregnancy to see if the baby has a hemolytic disease.

Some babies who have hemolytic disease will have uncomplicated pregnancies and be born at a normal gestation. Other babies will have difficulty and require the birth to be done earlier. Blood transfusions can be given both before and after birth for these severely affected infants.

Complications associated with Rh-positive babies born to Rh-negative women include anemia, brain damage, heart failure, jaundice, stillbirth, and death after birth.

If you have questions about the Rh factor or whether or not you are in this group of women, ask your doctor or midwife for the results of your blood work.

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