O Negative Blood Group and Pregnancy

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What You Need to Know About Negative Blood Group and Pregnancy

One of the routine blood tests that you’ll have done in early pregnancy is a test to determine your blood group. Unless you’ve had major surgery or needed a blood transfusion, you might not know. But in pregnancy it’s important because your baby’s blood group may be different to yours. Let’s start off by understanding the different blood types and Rhesus factor.

What are the different blood types?

Your blood type is determined by genes from your parents. Each type is different based on which type of protein molecule is present on the surface of the red blood cells. There are 4 main blood types classified as the letters A, B, AB, or O.

What is Rhesus factor?

The Rhesus factor, or Rh factor refers to a type of protein found on the outside of blood cells. If you are + (positive) it means that your blood cells carry the Rh (rhesus) antigen. If you are – negative, they don’t carry the Rh (rhesus) antigen.
Altogether there  are 8 possible blood types and Rh factor combinations: A-, A+, B-, B+, AB-, AB+, O-, and O+.

Can a Rh negative mom have a positive baby?

Yes, the blood type is based on genes from both parents. so if your partner is positive, your baby may inherit the positive antigens. If you are O negative and your partner is for example A positive, it’s likely that your baby would be born with A blood type, as O blood type is recessive. Either way, you can get your baby’s blood tested at birth to determine their blood type and Rh factor.

Why is it important to know blood type and Rh factor? 

If you test Rh positive in pregnancy you won’t need another test. If you test Rh negative and your partner is positive, you will be advised to get a test called an antibody screen around 28 weeks to see if your blood has Rh antibodies

Why does negative blood type affect pregnancy?

Usually your Rh factor blood type isn’t an issue. But during pregnancy, being Rh-negative can be a problem if your baby is Rh-positive. If your (Rh negative)blood and your baby’s (Rh positive) blood mix, your body will start to make antibodies that can damage your baby’s red blood cells

Are Rh antibodies dangerous?

The antibodies produced aren’t a problem during your first pregnancy. Rh antibodies are harmless until your second or later pregnancies. If you carry another Rh-positive child, your Rh antibodies will recognize the Rh proteins on the surface of the baby’s blood cells as foreign. Your antibodies will pass into the baby’s bloodstream and attack those cells because it sees them as a foreign body.  This is called Rh incompatibility.  

Is there treatment available for Rh incompatibility? 

Yes, there is. If this is your first pregnancy (and you test Rh negative) you can have a blood test to check if you have any antibodies. If you test negative (no antibodies) your care provider may  recommend an injection called Rhogam which can be administered at 28 – 32 weeks of pregnancy to prevent your blood from creating antibodies. It’s important to know that Rhogam /Anti D is a sterilized solution made from human blood, which carries its own risks. If you choose not to have it, you can wait until your baby is born and only have the shot if your baby tests positive. If your baby  is positive, you’ll be advised to have the injection within 72 hours of your baby being born to prevent your body from forming antibodies in subsequent pregnancy. 

What if you test positive for antibodies? 

If you test positive for antibodies during pregnancy, the injection is ineffective and your care provider will monitor your pregnancy more closely. The main concern is that your baby becomes anaemic while still in utero. This can be treated with a blood transfusion via the umbilical cord but this is rare. Most often you will carry to term but your baby may require specialist care in the NICU to treat the anaemia with IV fluids and phototherapy. 

Knowing your blood group and that of your partner will help you to plan your care and assist you to make the right choices during pregnancy. 

Want to know more?

If you enjoyed this article, join me in The Due Date Club.  We have regular lively discussions about the choices available during pregnancy and a library packed with handy cheat sheets and printable to guide your decisions. 

Recommended reading

I highly recommend this book from Dr. Sarah Wickham Anti D explained. 


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