Rh Blood Type and Pregnancy: What You Need to Know

If you’ve recently found out you’re pregnant (or think you might be), you may hear your provider mention your “Rh factor” early on. It may come up during routine lab work, and can feel like just another box to check. But if you’re told you’re Rh negative, it can raise questions that aren’t always clearly explained.

Rh factor is a small detail in your blood, yet it can influence how your body responds during pregnancy. It doesn’t change how you feel day to day, and it doesn’t mean something is wrong. It simply affects how your immune system might react if your baby has a different blood type.

Understanding your Rh blood type in pregnancy helps you make sense of what’s happening in your body and what steps may be recommended along the way. With the right information and care, this is something providers monitor and manage every day, helping protect both you and your baby throughout pregnancy and beyond.

What Is Rh Blood Type in Pregnancy?

Your blood type is determined by specific markers on your red blood cells [1]. Most people are familiar with the ABO blood groups (A, B, AB, or O), but there’s another important marker called the Rh factor.

• If your blood has the Rh protein, you are Rh positive
• If your blood does not have it, you are Rh negative

You might hear this referred to by others as having an “AB-positive” blood type or being “O-negative.” This doesn’t have much bearing in your day-to-day life, other than when donating blood, but when it comes to Rh blood type pregnancy, what matters most is whether your Rh status is compatible with your baby’s.



What Does Rh Negative Blood Type Mean in Pregnancy?

If you are Rh negative, it simply means your blood lacks the Rh protein. This is not an illness or condition, but rather a natural variation in blood type.

Your baby’s Rh factor is determined by genetics. Specifically, genes that are inherited from both parents [2].

Here’s a simple breakdown:

• Each parent passes down one Rh gene to the baby
• The Rh-positive gene is dominant, while the Rh-negative gene is recessive

This means that if the baby inherits even one Rh-positive gene, they will be Rh positive.  The baby is only Rh negative if they inherit two Rh-negative genes (one from each parent)

So, if the mother is Rh negative (two negative genes), and the father is Rh positive, the baby could be either Rh positive or Rh negative, depending on the father’s genetics.

For example:

• If the father carries one positive and one negative gene, there’s about a 50% chance the baby will be Rh positive
• If the father carries two positive genes, the baby will almost always be Rh positive

In this situation, if you are Rh negative and your baby is Rh positive, your body may recognize your baby’s Rh-positive blood as foreign and begin creating antibodies against it [2]. This is called Rh incompatibility.

These antibodies matter because they can cross the placenta and attack your baby’s red blood cells. Red blood cells carry oxygen throughout the body, so when they are broken down, it can lead to problems like anemia, jaundice, and in more serious cases, complications that affect your baby’s organs [4].

And while most women don’t experience problems during their first pregnancy, issues are more likely in future pregnancies if not properly managed.

How Rh Blood Type Is Tested During Pregnancy

Testing your Rh factor is simple and routine. It’s usually done early in pregnancy through a standard blood test.

Here’s what you can expect:

• A small blood sample is taken
• Your blood type and Rh factor are identified
• Additional testing may check for existing antibodies

At Pregnancy Care Clinic, your initial pregnancy testing appointment can help confirm your pregnancy and guide you toward next steps, including medical follow-up. However, PCC does not perform RH testing.

How Can Rh Blood Type Affect Pregnancy?

So, how can Rh blood type affect pregnancy?

As we’ve said, if an Rh-negative mother carries an Rh-positive baby, her immune system may produce antibodies that attack the baby’s red blood cells. 

Potential effects on the baby can include [4]:



• Mild to severe anemia
• Jaundice (yellowing of the skin and eyes)
• Swelling (in more serious cases)
• Complications after birth if untreated

That said, modern medical care has made serious complications from Rh incompatibility much less common.

Treatment Options for Rh Incompatibility

If you are Rh negative, there is a safe and effective way to prevent complications.

The most common treatment is an injection called Rh immunoglobulin (RhIg), often known by brand names like RhoGAM [3]. The injection prevents your body from forming harmful antibodies, and protects current and future pregnancies.

It is typically given at multiple points during and after pregnancy, including:



• Around 28 weeks of pregnancy
• Within 72 hours after delivery (if the baby is Rh positive)
• After certain events like miscarriage, bleeding, or abdominal trauma

With this treatment, most women with Rh incompatibility go on to have healthy pregnancies and babies.

What Happens if Rh Incompatibility Is Untreated

Without treatment, Rh incompatibility can lead to a condition called hemolytic disease of the newborn (HDN) [4].

This occurs when:



• The mother’s antibodies attack the baby’s red blood cells
• The baby develops anemia and other complications

In severe cases, it can lead to:

• Organ damage
• Heart complications
• Stillbirth (rare, but possible without care)

That’s why early testing and treatment make such a big difference.

Rh Factor and Pregnancy: FAQs