CBSE Class 10 Answered

An Rh–negative woman can become sensitized if she is pregnant with an Rh–positive fetus.

During pregnancy, a small amount of blood from the foetus can cross the placenta into the woman's system. When this happens, a small number of pregnant women with Rh–negative blood who carry an Rh–positive foetus will react as if they were allergic to the foetus. These Rh–negative women become sensitized and make antibodies that attack the blood of the Rh–positive foetus. When this happens, the antibodies break down the fetal red blood cells. This causes anemia, which can lead to a serious illness, brain damage, or even death of the foetus or newborn.

Once formed, these antibodies do not go away. In a first pregnancy with an Rh–positive fetus, the baby often is born before the woman's body develops many antibodies, so there may be no serious problems.

In a second pregnancy with an Rh–positive fetus, these antibodies are more likely to cause anemia in the foetus. In most cases, the condition becomes worse in later pregnancies.