Pregnancy and Rh-Negative Blood

Reviewed by James Brann, MD
Rh is the protein, which is found on red blood cells. If you have this type of protein, you have Rh-positive blood type. If you don’t have this protein, you have Rh-negative blood type. Whether you are positive or negative doesn’t impact your health. However, there are some problems during pregnancy if a mom is Rh-negative and her baby has Rh-positive blood type.
The good news is there is medicine to help prevent most of the problems. A doctor will test your blood as part of your first prenatal visit. This includes testing your blood type.

Problems with Rh-negative blood

There are certain problems that may develop when a mom has Rh-negative blood and her still unborn child has Rh-positive blood.

Usually, a mom and baby’s blood doesn’t mix during pregnancy, however if can right after delivery. If a small amount of your baby’s blood were to get in your blood vessels during delivery, your immune system would start making proteins called antibodies. In your next pregnancy, these antibodies run the risk of crossing the placenta and possibly damaging your future baby’s red blood cells. This could lead to anemia. That’s when someone doesn’t have enough red blood cells. When this happens, your child could make more red blood cells, but possibly not enough to help prevent anemia.

Knowing baby’s blood type

It’s sometimes difficult to know your unborn child’s blood type. If you know the father’s blood type, though, you might be able to figure it out. If both the mom and dad have Rh-negative blood, your baby will also have Rh-negative blood.

If your baby’s father is Rh-positive, though, your baby could have either. In this case, your doctor will treat your child as if the child has Rh-positive blood. This way, they can help prevent any problems.

What’s next?

If you are Rh-negative, your doctor will want to do blood tests while you’re pregnant to check and see if you have antibodies in your blood. If you don’t have them, and your baby is likely Rh-positive, your doctor will want to give you medicine. This type of medicine keeps your body from making the antibodies that could potentially attack your child’s red blood cells. This can ward off anemia and other problems.
This type of medicine is called anti-D immune globulin. The sample brand name is RhoGAM, and it’s normally a shot that you get during your final trimester. Once your baby is delivered, your doctor will want to test your child’s blood type. If your child is Rh-positive, he or she will give you a second dose of anti-D immune globulin not long after delivery. If you’re Rh-negative, you won’t need a second dose.

If you’re Rh-negative you may get the anti-D immune globulin at other times, though. This sometimes happens if a woman:
  • Bleeds during her pregnancy
  • Has an amniocentesis test or chorionic villus sampling (CVS)
  • Has her pregnancy end with an abortion
  • Has her pregnancy end in a miscarriage
  • Has an ectopic pregnancy (grows in the wrong place)

Antibodies in your blood

If a woman already has antibodies in her blood, anti-D immune globulin won’t help and your doctor won’t give you this medicine.

You will have several kinds of tests to monitor your baby while you’re pregnant. If you develop anemia, or have other problems, you doctor will talk to you about the possible treatments.

Future pregnancies

If you do get pregnant again in the future, you’ll need the treatment again. Rh-negative women have to be treated with anti-D immune globulin each pregnancy, just so long as they don’t have antibodies in their blood.

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