May 2024

Rhogam: The Miracle Shot

A pregnant person might not know their exact blood type, but they’ll usually know if it’s the kind that needs “the shot.” Calling it “the shot” doesn’t really convey the amazing protection offered against Rh isoimmunization by the injection of Rho(D) Immune Globulin (RhIG), also known as RhoGAM

Why is the Rhogam shot needed? Just a few generations ago, over 10,000 babies a year were lost to Rh incompatibility in the United States. Until 1968 there was nothing to prevent this disease and the many sad outcomes related to it: miscarriage or stillbirth, and extremely ill newborns.

What is Rh isoimmunization or incompatibility? Everyone’s blood type, A, B, AB, or O, is also typed as either negative (-) or positive (+). This indicates the Rh factor; the presence or absence of the Rhesus D antigen.

If an Rh(-) person, pregnant with an Rh(+) baby, becomes exposed to their baby’s blood (most often at delivery), it can trigger antibodies to develop that will attack the antigens in the RH(+) blood.

When exposure happens at delivery, that baby will usually be fine, as it takes time for the antibodies to develop, but if the mother’s body goes on to develop antibodies to the Rh antigens she will be considered isoimmunized or to have Rh incompatibility.

Her antibodies will destroy any Rh(+) red blood cells that might show up in her body with a future pregnancy.

Before RhIG injections were available, some families seemed to be plagued by pregnancy loss, often after a healthy, first child. The Rh factor in blood wasn’t identified until 1940, so they would not have known the series of apparently random pregnancy loss was due to Rh incompatibility triggered by a previous pregnancy.

Many newborns died or had lifelong disabilities from the disease. Fortunately, the incidence of Rh incompatibility has decreased dramatically and treatment options have improved significantly.

How does the shot work? The RhIG injection prevents the development of these antibodies. Researchers discovered that if the shot was given to an Rh(-) mother within 72 hours of giving birth to an Rh(+) baby, these dangerous antibodies did not develop, therefore future pregnancies were protected.

It is now routine to immediately test the cord blood of every baby born to an Rh(-) person, so they can receive an injection to prevent isoimmunization if the baby is Rh(+). (If the baby is Rh(-) no shot is needed.)

As additional prevention, any pregnant Rh(-) person is offered the RhIG injection at 28 weeks gestation, even though the baby’s blood type is not known yet, to protect against possible blood mixing in the last weeks of pregnancy.

Occasionally, some people choose to skip the 28 week injection and wait to get the shot only if the baby is Rh+ at birth or there is an indication of bleeding/blood mixing before then. Parents should thoroughly discuss all options with their care provider as they make choices about their care.

Another indication for an RhIG injection to prevent possible isoimmunization is anytime there might be fetal/maternal blood mixing, including miscarriage, abortion, ectopic pregnancy, abdominal trauma, amniocentesis, or chorionic villus sampling in a pregnant Rh(-) person.

Today we are far removed from the danger and heartache of Rh isoimmunization that was common decades ago. What is now a routine shot was once considered the miracle of Rhogam®.

By Laura Maxson LM

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