How do I find out my blood type and Rh factor?

You do not have to find it on your own. Your blood type and Rh factor are checked with a routine blood draw early in prenatal care, and your provider will tell you the result. If you are not sure what your type is, ask at your next visit, because it will be in your prenatal labs.

Rh immune globulin, often called RhoGAM, is considered safe and is a standard, routine part of prenatal care for people who are Rh negative. It has been used for a long time and has made hemolytic disease of the newborn from Rh incompatibility rare where this care is followed. Your provider can answer any specific questions you have about it.

When is the shot given?

According to ACOG, if you are Rh negative and not already sensitized, you are typically offered a dose at around 28 weeks and another within 72 hours after birth if your baby is Rh positive. A dose is also given after events that can mix blood, such as miscarriage, ectopic pregnancy, bleeding, amniocentesis, or abdominal trauma. Call your provider after any bleeding or abdominal injury so they can decide if a dose is needed.

Why is my first baby usually fine but a future one might be at risk?

In a first pregnancy, blood most often mixes during delivery, leaving little time for antibodies to form and reach that baby, so the first Rh-positive baby is usually not affected. But once antibodies form they stay, and in a later pregnancy they can cross the placenta and harm a future Rh-positive baby. The shot prevents those antibodies from ever forming, which protects future pregnancies.

Prenatal care

Rh negative in pregnancy and how RhoGAM protects your baby

June 29, 2026 · 8 min read

Early in your prenatal care, your provider checks your blood type. One of the things they are looking for is the Rh factor, a protein that is either present (Rh positive) or absent (Rh negative) on your red blood cells. If you are Rh negative and your baby is Rh positive, your body can react to your baby's blood in a way that matters more for future pregnancies than the current one. The good news is that medicine has turned this into a solved problem. A simple, safe, routine shot called Rh immune globulin, often known by the brand name RhoGAM, prevents the reaction almost entirely. This article explains the Rh factor, what incompatibility means, and how the shot protects your baby. It is general education, not medical advice, so call your provider with any concerns about your blood type or bleeding.

A mother holding her child in a warm, supportive moment

Blood types and the Rh factor

Your blood type has two parts. The first is the letter group: A, B, AB, or O. The second is the Rh factor, written as a plus or minus sign after the letter, so you might be A positive or O negative. The Rh factor refers to a protein, sometimes called the Rh or D antigen, that sits on the surface of red blood cells. If you have that protein you are Rh positive, and if you do not you are Rh negative. Being Rh negative is perfectly normal and is not a disease or a problem on its own; it simply describes your blood. This is one of the first things checked in prenatal care, usually with a blood draw at one of your early visits, because knowing your type lets your care team plan ahead. If you do not know your blood type, you do not need to track it down yourself, because your routine prenatal labs will show it and your provider will tell you the result.

What Rh incompatibility means

Rh incompatibility happens when an Rh-negative pregnant person is carrying an Rh-positive baby, which can occur when the other biological parent is Rh positive. The two blood types do not normally mix during a healthy pregnancy because the placenta keeps them separate. The concern is that a small amount of the baby's Rh-positive blood can cross into the pregnant person's bloodstream, most often during birth, but also during certain events that can mix blood. When an Rh-negative immune system meets Rh-positive blood, it can treat that protein as foreign and start making antibodies against it. The American College of Obstetricians and Gynecologists (ACOG) describes this process, called Rh sensitization, as the root of the problem. The key thing to understand is that the antibodies usually do not form fast enough to affect the pregnancy where the mixing happened. Instead, they stay in the body and can become a problem for a future Rh-positive baby.

Why the first pregnancy is usually fine but a future one is at risk

In a first pregnancy with an Rh-positive baby, the most common time for blood to mix is during delivery, near the very end. By then there is little time left for antibodies to build up and reach the baby, so a first Rh-positive baby is usually not affected. The trouble starts afterward. Once an Rh-negative immune system has been sensitized and has made antibodies, those antibodies remain. In a later pregnancy with another Rh-positive baby, the antibodies can cross the placenta and attack the baby's red blood cells. According to ACOG, this can cause hemolytic disease of the newborn, where the baby's red blood cells are destroyed faster than they can be replaced, leading to anemia and other complications that can be serious. This is why prevention is aimed not only at the current pregnancy but at protecting every pregnancy that may come after it. Stopping sensitization before it starts is the whole strategy.

How RhoGAM prevents the problem

The prevention is Rh immune globulin, frequently called by the brand name RhoGAM. It is a shot that keeps an Rh-negative immune system from reacting to Rh-positive blood, so it never starts making those lasting antibodies. According to ACOG, if you are Rh negative and not already sensitized, you are typically offered a dose at around 28 weeks of pregnancy, and another dose within 72 hours after birth if your baby is confirmed to be Rh positive. The 28-week dose covers the rest of pregnancy, and the dose after birth covers the larger blood mixing that can happen during delivery. A dose is also given after events that can mix blood, including miscarriage, ectopic pregnancy, bleeding during pregnancy, amniocentesis or similar procedures, and abdominal trauma such as a fall or car crash. The timing matters, which is why prompt care after any of these events lets your provider decide whether you need a dose.

The antibody screen and the rest of your Rh testing

Along with checking your blood type, your prenatal labs include an antibody screen, sometimes called an indirect Coombs test. This test looks for whether your blood already carries antibodies, including Rh antibodies, which tells your provider whether you are still a candidate for the preventive shot or have already been sensitized in the past. For most Rh-negative people the screen is negative, meaning the RhoGAM strategy applies and prevention can do its job. If the screen shows antibodies are already present, your care simply shifts to closer monitoring of the baby, which your provider will explain. After your baby is born, the baby's blood is checked to find out whether the baby is Rh positive, because the dose after birth is only needed if the baby is Rh positive. None of this requires you to memorize the steps. The point is that the testing is routine, your team handles the timing, and the results guide a clear plan.

Safe, routine, and a reason for reassurance

It is worth saying plainly that Rh immune globulin is considered safe and is a standard, routine part of prenatal care for Rh-negative pregnancies. Before this prevention existed, Rh disease was a major and sometimes devastating cause of harm to newborns. Today, because the shot is given on a reliable schedule, hemolytic disease of the newborn from Rh incompatibility has become rare in places where this care is followed. That is the reassuring center of this topic: being Rh negative is common, it is not your fault, and when you keep your prenatal appointments and get the shots as recommended, the risk to future babies is brought very low. If you are Rh negative, you do not need to worry your way through pregnancy. You need a blood type on file, an antibody screen, the doses at the right times, and a quick call to your provider after any bleeding or abdominal injury so a dose can be added if needed.

How Materna fits in

Materna does not run your labs or give the shot; your prenatal team does that. What Materna does is keep your records in one bilingual place so details like your blood type, your antibody screen result, and the dates of your RhoGAM doses are easy to find and travel with you between visits and providers. The Mommy Passport is free for patients, paid by providers, and Spanish first, and clinical and safety information like this is never paywalled. Materna serves families in Arizona, California, Texas, and Pennsylvania. This article is general education, not medical advice. Call your provider with any concerns about your blood type, and call right away after any bleeding or abdominal trauma so they can decide whether you need a dose. For a medical emergency call 911, and for mental health support you can reach the 988 Suicide and Crisis Lifeline.

Learn how Materna supports your prenatal care

Frequently asked questions

How do I find out my blood type and Rh factor?: You do not have to find it on your own. Your blood type and Rh factor are checked with a routine blood draw early in prenatal care, and your provider will tell you the result. If you are not sure what your type is, ask at your next visit, because it will be in your prenatal labs.
Is RhoGAM safe?: Rh immune globulin, often called RhoGAM, is considered safe and is a standard, routine part of prenatal care for people who are Rh negative. It has been used for a long time and has made hemolytic disease of the newborn from Rh incompatibility rare where this care is followed. Your provider can answer any specific questions you have about it.
When is the shot given?: According to ACOG, if you are Rh negative and not already sensitized, you are typically offered a dose at around 28 weeks and another within 72 hours after birth if your baby is Rh positive. A dose is also given after events that can mix blood, such as miscarriage, ectopic pregnancy, bleeding, amniocentesis, or abdominal trauma. Call your provider after any bleeding or abdominal injury so they can decide if a dose is needed.
Why is my first baby usually fine but a future one might be at risk?: In a first pregnancy, blood most often mixes during delivery, leaving little time for antibodies to form and reach that baby, so the first Rh-positive baby is usually not affected. But once antibodies form they stay, and in a later pregnancy they can cross the placenta and harm a future Rh-positive baby. The shot prevents those antibodies from ever forming, which protects future pregnancies.