What Happens When You Get a RhoGAM Shot

Depending on what blood type you and your baby are, you may need a RhoGAM shot during your pregnancy. What does that mean exactly? Well, early in your pregnancy, you'll take a blood test to determine if your blood is Rh-positive or Rh-negative. Rh, or rhesus, is a protein that rides along on the surface of the red blood cells of about 85% of people. If the protein is found on your red blood cells, you are Rh-positive—and if it's not there, you're Rh-negative.

The presence or absence of the rhesus protein really only matters when you're pregnant with your second or subsequent child. Keep reading to learn the reason, and figure out what to expect if you need a RhoGAM shot.

What Is the RhoGAM Shot?

The RhoGAM shot is an injection made up of antibodies called immunoglobulin that stop an Rh-negative person's immune system from creating antibodies to Rh-positive blood during pregnancy. The shot effectively protects the red blood cells of a future Rh-positive fetus from being attacked by its Rh-negative gestational parent's antibodies.

According to the product website, "RhoGAM prevents the Rh-negative mother from making antibodies during her pregnancy. As long as the Rh-negative mother receives RhoGAM appropriately during every pregnancy, her babies are at very low risk of developing [anemia]."

Sheila Chhutani, M.D., of Gyn/OB Associates in Dallas, Texas, tells Parents: "RhoGAM is immunoglobulin, or manufactured antibodies, that will attach to the rhesus protein in the mother's blood, not allowing her body to process or 'see' that protein to start manufacturing her own antibodies. The RhoGam does not cross the placenta and will not harm the baby."

Why Do Some Pregnant People Need a RhoGAM Shot?

When a pregnant person who is Rh-negative (their red blood cells have no rhesus protein) is carrying a fetus whose blood is Rh-positive (their red blood cells do have rhesus protein), there is a risk that if the parent and fetus's blood comes into contact with one another, the parent's immune system may produce antibodies that attack Rh-positive red blood cells.

Think of antibodies as little warrior cells that go off to do battle against invading forces. Any time you are exposed to an antigen, your body produces antibodies specific to that antigen, so if it is exposed again, your immune system is ready to fight it off.

This is why your Rh factor isn't an issue during first pregnancies. It isn't until second and subsequent pregnancies when antibodies are already built up, that Rh incompatibility can cause problems. Indeed, these antibodies can cross the placenta and attack an Rh-positive fetus's red blood cells. This can cause the baby to develop anemia, and in severe cases, result in miscarriage.

Since you and your baby don't share a circulatory system, there are only a few circumstances during pregnancy when fetal blood can come into contact with maternal blood. Tami Prince, M.D., of Women's Health and Wellness Center of Georgia, says cross-contamination can occur "during early pregnancy bleeding, procedures such as an amniocentesis or CVS (chorionic villus sampling), direct abdominal trauma, ectopic pregnancy, miscarriage, or blood transfusion with mismatched blood typing."

To prevent complications, "it is critical that an Rh-negative woman be treated with Rh immunoglobulin if bleeding occurs in order to prevent antibody formation," Dr. Prince says. Luckily, there's an injection that Rh-negative pregnant people can receive to counteract Rh incompatibility: the RhoGAM shot.

When Is the RhoGAM Shot Given?

According to Dr. Chhutani, the RhoGAM shot is typically given at 28 weeks gestation because it will last for about 12 weeks. "At delivery, if the newborn is Rh-positive, the mother will receive another dose of RhoGAM," Dr. Chhutani adds.

This last injection is given just in case there was any cross-contamination of blood from the baby to the birth parent during delivery. One last dose of immunoglobulin will prevent the gestational parent's body from producing antibodies that may place future pregnancies at risk.

RhoGAM Shot Side Effects

Side effects from the RhoGAM shot are usually mild and don't harm the baby or affect breastfeeding. They might include swelling and/or redness at the injection site, itching at the injection site, and mild fever. Less common side-effects can include allergic reaction, headache, joint or muscle pain, and fatigue. If any of these are experienced, you should talk to your doctor.