How is Rh incompatibility diagnosed?

For most women, simple blood tests diagnose Rh incompatibility. If you become pregnant, your obstetrician will test you to determine if you are Rh-negative. Doctors usually do this test with your routine first trimester blood work. It may be done earlier if you have vaginal bleeding.

  • If you have Rh-negative blood, your doctor may order another blood test, called an antibody screen. This test checks whether your blood contains Rh antibodies. If your antibody screen comes back positive, you are at risk for Rh incompatibility.
  • If you are Rh-negative and your antibody screen is negative, you will be given Rh immunoglobulin (RhIg) to prevent antibody formation. This is typically given around 28 weeks and within 72 hours of delivery. You may get a dose in early pregnancy if you have bleeding or other complications.

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