Srinidhi is pregnant for the first time. She knew that she was Rh negative. When she went for her first antenatal checkup, her obstetrician checked and found out that her husband was Rh positive. Srinidhi and her husband had many questions. Would this difference in their Rh factor affect the baby? Would she have to take any precautions? Would this affect her next pregnancy? Srinidhi and her husband need not worry.

The Rh factor

There are four blood types: A, B, AB, and O. Each of the four blood types is additionally classified according to the presence of another protein (antigen) on the surface of red blood cells that indicates the Rh factor. If this antigen is present, you are classified as being Rh positive. If this antigen is absent, you are considered Rh negative. About 85% of Indians are Rh positive. This percentage varies in some ethnic communities. If a woman who is Rh negative and a man who is Rh positive conceive a baby, there is the potential for the baby to have a health problem.

Approximately half of the children born to an Rh-negative mother and Rh-positive father will be Rh positive. The problem arises only if the baby developing inside the Rh-negative mother has Rh-positive blood, inherited from the father. This problem is called Rh incompatibility. Luckily, Rh incompatibility causes harmful effect in only 10% of women who are affected.

Rh incompatibility usually does not lead to a problem in the first pregnancy. In the subsequent pregnancies, however, problems can arise for the child growing in the uterus.

How does Rh sensitisation occur?

The exposure of an Rh negative woman to Rh positive blood is called sensitisation. During delivery, the mother's and baby's blood can get mixed. The mother's body identifies the Rh protein as a harmful substance and will begin producing antibodies.These antibodies later cause destruction of any Rh positive blood cells they encounter.

An Rh negative woman is tested for the presence of these antibodies on the confirmation of pregnancy and then usually in the 5^th and 8^th month. This simple blood test is called an indirect Coomb’s test. If a woman has antibodies in her blood, the test will be called positive. If she has no Rh antibodies, then the indirect Coomb’s test will be negative.