How Your Rh Factor Can Affect Your Pregnancy

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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 incompatibility. 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 type of protein on the surface of red blood cells. When present, a persons blood type is Rh-positive (such as A+ or O+). When the Rh protein is absent, the blood type is Rh-negative (such as AB- or B-).

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

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

When the Rh Factor May Negatively Affect a Pregnancy

While the mother's and fetus's blood systems are separate, there are times when the blood from the fetus can enter into the mother's bloodstream. If this happens, the mother's immune system identifies the Rh-positive blood as an intruder and responds by making antibodies to destroy it. This response is called Rh sensitization.

The antibodies in an Rh-sensitized mother can cross the placenta and attack the fetus's Rh-positive blood. These antibodies can break down and destroy the fetus's red blood cells (hemolysis), leading to anemia. This condition is called hemolytic disease or hemolytic anemia.

In severe cases, hemolytic disease can cause high levels of bilirubin in the blood (hyperbilirubinemia), brain damage, and even death.

Sensitization can 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. Rh immunoglobulin (RhoGAM) is a prescription medicine given by intramuscular injection that stops an Rh-negative mother from making antibodies that attack Rh-positive red cells.

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

Because 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 is usually given around week 28 of pregnancy and lasts about 12 weeks. If the fetus is Rh-positive, the mother will also be given RhoGAM within 72 hours of birth. 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

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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5 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Dulay AT. Merck Manual Professional Version. Erythroblastosis Fetalis.

  2. American College of Obstetricians and Gynecologists. The Rh Factor: How it Can Affect Your Pregnancy.

  3. Costumbrado J, Mansour T, Ghassemzadeh S. Rh Incompatibility. Treasure Island, FL: StatPearls Publishing.

  4. RhoGAM [package insert]. Melville, NY: Kedrion Biopharma Inc.

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By Robin Elise Weiss, PhD, MPH
Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor.