Key takeaways:
People who are Rh-negative (have a negative blood type) should have a RhoGAM shot during the 28th week of their pregnancy.
RhoGAM is effective in preventing Rh isoimmunization, a reaction that can cause harm to an unborn baby.
RhoGAM has been in use for decades and has a strong safety record.
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If you’re currently pregnant, you may have heard that you might need a RhoGAM shot. But you may have many questions about what the RhoGAM shot is, how it works and whether it’s actually necessary.
Here’s what you should know about getting a RhoGAM shot in pregnancy and why it’s recommended.
What is RhoGAM?
RhoGAM is a medication that contains Rh immune globulin. RhoGAM is the brand name of this medication and is given as an injection. There are other brand names and even a generic Rh immune globulin. But RhoGAM has become the popular name when referring to Rh immune globulin.
RhoGAM is an antibody made from donated blood. And like all antibodies, the RhoGAM shot works by protecting against something that can cause harm to the body. In this case, it’s used as protection to keep your body from forming anti-D antibodies in pregnancy.
Do I need to get a RhoGAM shot during pregnancy?
If you’re Rh-negative, you may need a RhoGAM shot during pregnancy if there’s a possibility you’re carrying a fetus with Rh-positive blood. The RhoGAM shot stops your body from making anti-D antibodies that can attack your unborn baby’s red blood cells. This process is called Rh isoimmunization and can cause serious health problems in babies. But with RhoGAM, the risk of this complication drops to almost zero.
If you’re Rh-negative and have already made anti-D antibodies in a previous pregnancy, the RhoGAM shot isn’t helpful and won’t be needed.
What is the Rh factor?
The Rh factor is a protein that’s found on the surface of red blood cells. There are many proteins on the surface of red blood cells. But not everybody has the Rh factor.
Most people are familiar with AB antigens and the Rh factor, even if they don’t realize it. AB antigens determine a person’s blood type. The Rh factor determines whether a person has a negative or positive blood type.
People who have the Rh factor on their red blood cells have a “positive” blood type (Rh-positive), including:
A+
B+
O+
AB+
People who don’t have the Rh factor on their red blood cells have a “negative” blood type (Rh-negative), including:
A -
B -
O -
AB -
Rh-negative blood type is less common — present in only up to 15% of people. Your Rh factor doesn’t matter much in your day-to-day life, and it doesn’t affect your health. The only time your Rh factor matters is if you need a blood transfusion or if you’re pregnant.
People with a negative blood type can form anti-D antibodies if they’re exposed to a positive blood type (which usually only happens when someone is pregnant). Anti-D antibodies attack red blood cells that have the Rh factor on them.
In short, if you’re Rh-negative and you’re pregnant, you can develop antibodies that attack your baby’s red blood cells. This can lead to serious health issues for an unborn baby.
When is RhoGAM given?
If you’re Rh-negative and there’s a risk your fetus has Rh-positive blood, it’s recommended to get your RhoGAM shot around your 28th week of pregnancy. You may also need a second dose after you deliver your baby if your baby is confirmed to have Rh-positive blood.
People who are pregnant and Rh-negative might also need a RhoGAM shot if they have:
An invasive procedure during pregnancy like an operation or an amniocentesis
Any trauma to the abdomen area during pregnancy, like being in a car accident
An abortion, miscarriage, or fetal loss that happens after the 12th week of pregnancy
Bleeding during pregnancy
Manual attempts to change a baby from the breech position
The Rh-positive blood type is very common, and it’s a higher likelihood you may be carrying an Rh-positive fetus. So, many healthcare professionals may offer RhoGAM to you automatically if you’re pregnant and Rh-negative. But if you’re Rh-negative and it’s confirmed that the fetus is Rh-negative or the biological father is known to be Rh-negative, RhoGAM isn’t needed.
When is it too late to get a RhoGAM shot?
If you’re pregnant, Rh-negative, and haven’t formed anti-D antibodies on your own, it’s never too late to get your RhoGAM shot.
But it’s best to get your RhoGAM shot between 28 and 32 weeks so that the medication has a chance to work before you go into labor.
If you need a RhoGAM shot after your delivery or because you had a procedure, a miscarriage, or an accident, you must receive your shot within 72 hours. Otherwise, the medication may not work.
Keep in mind that the RhoGAM shot is used to prevent anti-D antibodies from forming. If you’ve formed antibodies in a previous pregnancy, the RhoGAM shot won’t be effective. Your healthcare team will typically do an antibody screen in pregnancy to check if you’ve made any antibodies if it’s possible your fetus has Rh-positive blood.
When to get RhoGAM shot during a second pregnancy?
The timing of your RhoGAM shot stays the same no matter what pregnancy you’re in. You should receive your shot around your 28th week of pregnancy or sooner if you have any procedures or bleeding.
If you have a negative blood type, and have a risk of carrying a fetus that has Rh-positive blood, you’ll need a RhoGAM shot during every pregnancy. In fact, it’s even more important to get the shot during subsequent pregnancies. That’s because if you had a baby with an Rh-positive blood type, you were exposed to your baby’s Rh-positive blood during your delivery.
Why do only Rh-negative people need a RhoGAM shot during pregnancy?
If you’re Rh-negative and your baby is Rh-positive, you can develop antibodies against your baby’s blood. This is called Rh isoimmunization.
Rh isoimmunization only happens if you’re Rh-negative and your baby is Rh-positive. If you’re Rh-positive, this reaction doesn’t happen, regardless of whether your baby is Rh-positive or Rh-negative. The reaction also doesn’t happen if you and your baby are both Rh-negative.
When you’re pregnant, some of your baby’s blood crosses over the placenta and into your bloodstream. If you’re Rh-negative and your baby is Rh-positive, your immune system will make antibodies when it comes in contact with your baby’s blood. The more of your baby’s blood that crosses over, the more antibodies your body will make.
Your antibodies can then cross the placenta and attack your baby’s red blood cells. When this happens, your baby can develop anemia. While many babies only develop mild anemia, others can have severe anemia. This can lead to multiple complications during pregnancy or after birth.
The RhoGAM shot stops your body from creating these antibodies, which keeps your baby safe. Before RhoGAM was invented in the 1960s, 10,000 babies died every year from Rh isoimmunization, and many more suffered from severe brain injuries.
Does RhoGAM cause side effects?
It’s possible for RhoGAM to cause side effects like any other medication. These can range from mild symptoms like redness and swelling at the injection site to more severe reactions like anaphylaxis.
RhoGAM is generally regarded as safe and the benefits are believed to outweigh the risks. Based on all available data, RhoGAM isn’t harmful to the fetus.
What happens if you don’t get a RhoGAM shot?
Classic studies show that people who are Rh-negative have about a 1 in 5 chance of developing Rh isoimmunization. It’s hard to predict in advance who might have that complication.
RhoGAM has been in use for decades and is one of the most commonly used medications in the world. But there are risks and benefits that come with any decision, especially one that involves your health.
It’s a good idea to discuss any concerns about RhoGAM with your healthcare team so they can help you make the best decision for you and the health of your baby.
Frequently asked questions
Rh-negative blood is rare in general, regardless of race. It’s estimated that only up to 15% of people are Rh-negative.
No, it’s not possible for two biological parents who are Rh-negative to produce an Rh-positive child.
Of the widely known blood groups, the Rh-negative blood types are the least common in the population. But keep in mind that there are many blood proteins that determine how rare a blood type may be.
Rh-negative blood is rare in general, regardless of race. It’s estimated that only up to 15% of people are Rh-negative.
No, it’s not possible for two biological parents who are Rh-negative to produce an Rh-positive child.
Of the widely known blood groups, the Rh-negative blood types are the least common in the population. But keep in mind that there are many blood proteins that determine how rare a blood type may be.
The bottom line
RhoGAM is an immunoglobulin that prevents Rh isoimmunization when an Rh-negative mother is pregnant with an Rh-positive fetus. Rh isoimmunization is when a pregnant person’s antibodies attack the blood cells of their unborn fetus. Though uncommon, this can lead to serious illness in the baby.
Since there’s no cure or treatment for Rh isoimmunization, the focus is on preventing it from ever happening by using RhoGAM. RhoGAM is effective and has been safely used for decades. If you’re pregnant and Rh-negative, talk to a healthcare professional about your need for a RhoGAM shot.
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References
American College of Obstetricians and Gynecologists. (2017). Prevention of Rh D alloimmunization.
American College of Obstetricians and Gynecologists. (2025). The Rh factor: How it can affect your pregnancy.
American Red Cross. (n.d.). Facts about blood and blood types.
American Red Cross. (2026). What is the Rh factor? Why is it important?
Dean, L. (2005). Blood groups and red cell antigens. National Center for Biotechnology Information.
Goldman, J. A., et al. (1972). Prevention of Rh immunization after abortion with Anti-Rh (D)-immunoglobulin. Obstetrics and Gynecology.
Kedrion Biopharma Inc. (2025). RhoGAM ultra-filtered plus (human rho- d immune globulin injection, solution Micrhogam ultra-filtered plus (human rho- d immune globulin injection, solution) [package insert]. DailyMed.
MedlinePlus. (2025). Red blood cell antibody screen.
Neighbor, J. (2018). RhoGAM at 50: A Columbia drug still saving lives of newborns. Columbia University Irving Medical Center.
Yoham, A. L., et al. (2023). Rho(D) immune globulin. StatPearls.
