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Your blood is typed according to the presence or absence of certain markers found on red blood cells and in the plasma. These markers allow your body to recognize blood as its own. One of these markers is the Rh factor. If your blood contains the Rh factor, you're Rh positive. If not, you're Rh negative.
Testing for Rh factor
If you are Rh negative and your baby is not, you could develop antibodies - similar to having an allergic reaction - to your baby's Rh positive blood. This can happen if your blood and your baby's blood mix at birth, during an amniocentesis test, or if bleeding occurs in your pregnancy. This can cause serious illness or even death for your next baby.
Because this condition can be prevented, it is seldom seen today. All pregnant women have a blood test during early pregnancy to determine their blood type and Rh-factor. If you're Rh negative you will receive an injection of Rh immune globulin (RhIg). This will prevent you from forming antibodies and causing possible harm to your next baby.
- at about 28 weeks gestation
- after birth if your baby is Rh positive
- after an amniocentesis
- if you have any vaginal bleeding