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Rh Sensitization During Pregnancy - Topic Overview

All pregnant women get a blood test at their first prenatal visit during early pregnancy. This test will show if you have Rh-negative blood and if you are Rh-sensitized.

If you have Rh-negative blood but are not sensitized:

  • The blood test may be repeated between 24 and 28 weeks of pregnancy. If the test still shows that you are not sensitized, you probably will not need another antibody test until delivery. (You might need to have the test again if you have an amniocentesis, if your pregnancy goes beyond 40 weeks, or if you have a problem such as placenta abruptio, which could cause bleeding in the uterus.)
  • Your baby will have a blood test at birth. If the newborn has Rh-positive blood, you will have an antibody test to see if you were sensitized during late pregnancy or childbirth.

If you are Rh-sensitized, your doctor will watch your pregnancy carefully. You may have:

  • Regular blood tests, to check the level of antibodies in your blood.
  • Doppler ultrasound, to check blood flow to the baby's brain. This can show anemia and how severe it is.
  • Amniocentesis after 15 weeks, to check the baby's blood type and Rh factor and to look for problems.

If you have Rh-negative blood but are not Rh-sensitized, your doctor will give you one or more shots of Rh immune globulin (such as RhoGAM). This prevents Rh sensitization in about 99 women out of 100 who use it.1

You may get a shot of Rh immune globulin:

  • If you have a test such as an amniocentesis.
  • Around week 28 of your pregnancy.
  • After delivery if your newborn is Rh-positive.

The shots only work for a short time, so you will need to repeat this treatment each time you get pregnant. (To prevent sensitization in future pregnancies, Rh immune globulin is also given when an Rh-negative woman has a miscarriage, abortion, or ectopic pregnancy.)

The shots won't work if you are already Rh-sensitized.

If you are Rh-sensitized, you will have regular testing to see how your baby is doing. You may also need to see a doctor who specializes in high-risk pregnancies (a perinatologist).

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