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Understanding your Blood Type in Pregnancy

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She Found Health
Understanding your Blood Type in Pregnancy

How does your blood type affect your pregnancy?

You’ve probably heard about the four main blood type classifications in humans: 

A       B     AB     O

In addition to these four main groups, people’s blood types can be further sub-categorized as being positive (+) or negative (-). What that refers to is the presence or absence of something called the Rh (Rhesus) Factor: a protein, or antigen, that is present on your red blood cells.

If your blood type is categorized as Rh-positive, you have the protein and RhD antigen. If your blood type is categorized as Rh-negative, you do not have the protein nor the RhD antigen. This distinction most matters when you are Rh-negative and your baby is Rh-positive.

Why does it matter? 

A problem is more likely to occur in people who are Rh-negative (you have a negative (-) sign after your blood type), which certain ethnic populations are more likely to be. To give you a quick breakdown based on ethnic descent:

  • Caucasian: ~ 15% - 17% of the population is Rh-negative
  • African: ~ 4% - 8% of the population is Rh-negative
  • First Nations/Inuit/Asian: ~ 5% or less of the population is Rh-negative

If a pregnant person is Rh-negative and they are exposed to Rh-positive blood cells, then their body actually makes antibodies against those RhD antigens.

How Can Exposure Happen?

An Rh-negative woman or pregnant person, pregnant with an Rh-positive fetus, can be exposed to fetal blood during pregnancy and birth in a number of different ways, including:

  • Delivery (vaginal or C-section)
  • Miscarriage (if the pregnancy is beyond around the seven week mark)
  • During any antepartum hemorrhage (bleeding during pregnancy)
  • Trauma (like a motor vehicle collision or a significant fall)
  • Procedures like chorionic villus sampling or amniocentesis
  • Ectopic pregnancy (a pregnancy outside of the uterus)
  • Molar pregnancy (a rare complication of pregnancy)
  • Less common non-pregnancy related exposures (such as ​​blood transfusions, bone marrow transplantations, and needle stick injuries)

What Happens with Exposure?

With exposure, the D antigen present in fetal cells is not recognized by the Rh-negative pregnant person's immune system, and is instead seen as something foreign, like a bacteria or virus. The immune system in its intelligence then makes anti-D antibodies, which can bind to those D antigens on the red blood cell of the Rh-positive fetus and break down those fetal red blood cells.

Generally, this does not affect the pregnancy during the time that the pregnant person was exposed to the fetal red blood cells, because the fetus is delivered before the pregnant person's body has enough time to produce those antibody antibodies. However, those anti-D antibodies persist for life and can cross the placenta.

This is where exposure becomes concerning, because it puts any future pregnancy with an Rh-positive fetus at risk for such things as hemolytic disease of the newborn - which is when these antibodies lead to breakdown of the fetus’s red blood cells, or other issues that can lead to the intrauterine death of your baby, in the worst case scenario.

The likelihood of exposure (Rh-negative pregnant person with an Rh-positive fetus) worldwide is about 276 out of 100,000 live births (0.276%). In developed countries alone, the likelihood is much lower with about 2.5 out of 100,000 live births (0.0025%) due to a high quality of prenatal care. While a variety of complications can occur with exposure that Drs. Sarah and Alicia discuss on the podcast, keep in mind that with appropriate screening and monitoring most are extremely rare and often treatable!

Prevention is Better than Cure?

Instances of severe illness due to exposure are very rare due to heightened prevention through screening and treatment!

An RhD blood type and antibody screen are done at the first prenatal visit and again at 28 weeks. If the pregnant person is Rh-positive, there is no risk of Rh incompatibility and we do not need to do anything about it! If they are considered Rh-negative, then we would recommend treatment to prevent the creation of those antibodies. And we do this at about 28 weeks, or if there was any sort of bleeding prior to that.

Treatment consists of giving an immunoglobulin to the pregnant person through a shot. It enters the bloodstream and sweeps up any of those antibodies that may have been created, possibly through tiny little micro bleeds among other things. We also recommend treatment because we have found in our practice that the pregnant person can be very “weakly” Rh-positive. This causes them at times to screen positive and other times negative, and we can’t rule out risk with certainty. Immunoglobulin treatment further decreases the risk in such instances.

It’s important to know how the immunoglobulin works - tune in to today’s podcast for a more thorough explanation! But in short, the treatment is given in the form of windrow: a sterile liquid prepared from pooled human plasma containing antibodies to D antigen found on Rh-positive red cells. It’s really important to understand that although this is considered a blood product, many, many steps are taken to confirm that there will be no risk of viruses being transmitted through injection, including donor screening, filtering, and treating the blood with a solvent and a detergent. Always have a discussion with your healthcare provider regarding if any treatment is right for you, but it’s important to know that there have been zero reports of infectious diseases transmitted by giving or getting windrow in pregnancy.

We hoped that this helped you learn a bit more about this somewhat complex physiologic system! And remember that even if you find yourself in a relatively rare Rh-negative position growing an Rh-positive fetus, there are low-risk and high-reward treatments available - just ask your healthcare provider!

Taking you from anxious and overwhelmed, to informed and confident in your childbirth experience! Learn more about our Pregnancy to Parenthood Online Prenatal Masterclass


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