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
- 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
- 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
- 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).