The Rh Factor in Pregnancy

Rh (or rhesus) factor is a protein found on the surface of red blood cells. If you inherited this protein, you’re Rh-positive. If you didn’t (and don’t have the protein), you’re Rh-negative.

Most people are Rh-positive, but being Rh-negative is only a potential problem during pregnancy.

If you’re Rh-negative and your fetus is Rh-positive, this incompatibility can lead to health problems for your fetus and require special care.

Here’s Why:

While your blood and that of your fetus usually don’t mix during pregnancy, it can sometimes happen—such as during childbirth or if you have bleeding or some kind of abdominal injury during pregnancy. Even this small amount of mixing can cause a problem, because your body may recognize your baby’s Rh-positive blood as foreign and start producing antibodies against it.

If those antibodies cross the placenta, they can also attack your fetus’s red blood cells, which can cause serious health problems in your baby.

Newborns affected by Rh-positive antibodies may have:

  • Anemia – when red blood cells are destroyed faster than the body can make them
  • Jaundice – when bilirubin (a pigment) builds up in the blood as red blood cells break down, causing the skin to look yellow
  • Swelling – which could result in heart failure or breathing problems

This health problem is less likely in a first pregnancy, because late in pregnancy (when the blood is most likely to mix) the expectant mother doesn’t have time before childbirth to make enough antibodies to be harmful to her fetus. But once those antibodies are made, they can threaten another Rh-positive fetus in a future pregnancy.

Rh incompatibility can also be a problem in:

  • ectopic pregnancy
  • miscarriage
  • induced abortion
  • trauma to the mother’s abdomen
  • during amniocentesis or certain other pregnancy screenings (though it’s rare)
How Is Rh Incompatibility Found and Treated?

If you have Rh-negative blood, your pregnancy healthcare provider may screen you (through a blood test) for the presence of Rh-positive antibodies, especially if this isn’t your first pregnancy. This screening usually occurs during

  • your first trimester,
  • week 28 of pregnancy and
  • at childbirth.

If you don’t yet have these antibodies, you’ll probably receive an injection of a blood product called RhIg (Rh immune globulin) at 28 weeks or within 72 hours of childbirth. This will prevent your body from producing those Rh antibodies. You’ll have to get the injections again in each subsequent pregnancy where the fetus has Rh-positive blood.

Be sure to talk with your healthcare provider about your Rh factor and whether you’ll need RhIg injections. These are not helpful if your body has already produced antibodies to Rh-positive blood.

If you can’t have the injections, your provider will closely monitor your pregnancy and the fetus. It’s possible that your baby will get a blood transfusion —through the umbilical cord during pregnancy or immediately or within 72 hours of childbirth, if necessary—to replace any blood cells damaged by the antibodies.

Learn more about the Rh factor in pregnancy.

Disclaimer: This page is not intended to provide medical advice about your child. Always seek the advice of a physician, qualified healthcare provider or child-development specialist with any questions you have about your child's health, medical condition or development. Never disregard, avoid or delay contacting a doctor or other qualified professional because of something you read here.

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