When you’re pregnant, routine blood tests give your care team important information to guide your pregnancy. One of these tests checks for Rh factor.
If the provider shares that you’re Rh negative, it’s normal to pause and wonder what that means, especially if this is your first pregnancy.
Rh factor can sound complicated but Rh testing is a standard part of prenatal care. It helps your care team prevent problems before they start.
With today’s screening and treatment, most people with Rh differences have healthy pregnancies and babies. Colleen Cagno, MD, a family medicine physician specializing in the care of pregnant people at Banner - University Medicine, explains what Rh factor is and what to expect if you are Rh-incompatible.
What is Rh factor?
Rh factor is a protein found in red blood cells. This specific protein is inherited (passed down from your biological parents). Not everyone carries Rh factor but most people do.
“If you are born with Rh factor protein, you are Rh positive,” Dr. Cagno said. “If you do not have the protein, you are Rh negative.”
Rh factor doesn’t change over time and does not affect your health on its own.
Why is Rh factor tested during pregnancy?
Rh factor testing is a routine part of first trimester prenatal care. Your provider wants to know your Rh status to plan for your baby’s safety.
If you are Rh-negative and your baby is Rh-positive, this difference is called Rh incompatibility.
For example:
- If you are Rh-negative and your partner is Rh-positive, your baby may have Rh-positive blood inherited from the father. Nearly half of children born to a Rh-negative mother and an Rh-positive father will be Rh-positive.
“Most of the time, this difference does not cause problems during the current pregnancy,” Dr. Cagno said. “The concern is that the pregnant person’s immune system may form antibodies after exposure to Rh-positive blood, which can affect future pregnancies because those antibodies can cross the placenta.”
However, small amounts of your blood and your baby’s blood can mix during:
- Delivery
- Miscarriage or abortion
- Bleeding in pregnancy
- Procedures like amniocentesis
- Abdominal trauma
What is Rh disease?
If antibodies form and a future pregnancy involves a Rh-positive baby, those antibodies can attack the baby’s red blood cells. This is called Rh disease, a hemolytic disease of the fetus and newborn.
According to Dr. Cagno, Rh disease can cause:
- Anemia in the baby before birth
- Jaundice after birth
- The need for closer monitoring or early delivery
Thanks to routine testing and preventive care, Rh disease is rare in the U.S. today.
How are Rh factor problems prevented?
Rh disease can be prevented with the medication Rh immune globulin (RhIG, RhoGAM). It works like a vaccine, preventing your immune system from producing antibodies against Rh-positive blood. Rh immune globulin is administered as a series of two injections, typically in the arm or buttocks.
“Rh immune globulin is typically given around 28 weeks of pregnancy after blood tests confirm antibodies have not already formed,” Dr. Cagno said. “The second shot is given within 72 hours after delivery if your baby is Rh positive. This protects future pregnancies.”
It may also be given earlier if there is a chance of blood mixing. “This includes pregnancy loss, ectopic pregnancy, abdominal trauma or certain procedures where blood mixing could occur,” Dr. Cagno said.
The medication has been used safely for decades and is a part of standard prenatal care.
New options: Testing fetal Rh status during pregnancy
A newer option is fetal Rh testing during pregnancy. This test uses a blood sample from a pregnant person to detect fetal DNA, which reveals the baby’s Rh type.
“If both the pregnant person and fetus are Rh negative, Rh immune globulin may not be needed,” Dr. Cagno said.
This test, often called non-invasive prenatal testing (NIPT) or cell-free DNA testing, can reduce unnecessary injections when the baby is already Rh negative. Most insurance companies cover NIPT but coverage may depend on medical necessity, your age or other risk factors. Contact your insurance provider to check your coverage.
How common are Rh complications today?
With routine prenatal care, Rh disease is now uncommon. Most Rh-negative pregnant people:
- Have healthy pregnancies
- Deliver healthy babies
- Do not experience complications related to Rh factor
“Knowing your Rh factor helps providers take simple, preventive steps to protect future pregnancies,” Dr. Cagno said. “With today’s care, serious complications are rare.”
Questions to ask your care team
You can stay informed by asking:
- What is my Rh factor?
- Will I need Rh immune globulin?
- When will I receive the injections?
- Does this affect future pregnancies?
- Are there any special precautions for my situation?
Bottom line
Rh factor is a standard part of prenatal care. Testing and treatment are routine, safe and highly effective.
If you are Rh-negative and pregnant, taking preventive steps helps ensure:
- Your pregnancy proceeds without complications
- A healthy outcome for your baby
- Protection for future pregnancies
Understanding your Rh factor and following your provider’s recommendations helps you focus on the most important part of pregnancy: welcoming your new baby.
If you have questions or concerns, speak with your health care provider or a Banner Health specialist.
