During pregnancy, one of the first blood tests you take checks for the Rh factor. Determined by genes passed on from your parents, the Rh factor is a type of protein that may appear on red blood cells. If you carry it, you're considered Rh-positive. If you don't, you're Rh-negative.
People are more likely to be Rh positive (85%) than Rh negative (15%). The problem is if the mother is Rh negative and the father is Rh positive. In that case, the following could occur:
- The baby may inherit the Rh protein from the father (your fetus would be Rh-positive).
- Your immune system might start producing antibodies against your baby's Rh protein. This occurs, because YOUR body considers this protein a foreign substance. This generally doesn't affect your first pregnancy, because your baby's blood doesn't mix with yours until delivery.
- In your next pregnancy, your anti-Rh antibodies could cross through the placenta into the baby's blood stream. Those antibodies will destroy the baby's red blood cells, causing mild-to-severe anemia to the fetus, or even death.
- To prevent Rh problems, mothers who are Rh negative receive a shot called Rhogam around 28 weeks or earlier if there were bleeding early on. Rhogam binds up any blood cells from your fetus before your body can recognize them and begin making antibodies.