Dr Maxwell Adeyemi

Blood is made up of three types of cells swimming in a body of fluid called plasma. One of these cells is the red blood cells, which are the most numerous and give blood its red colour. Red blood cells help to transport oxygen throughout the body and contain certain identification markers on their surface called antigens - tiny proteins that distinguish them for different purposes in the body. Rhesus is an antigen found on the surface of the red blood cells.

One of the important groups of antigens found on red blood cells are the antigens that determine our blood group. Some of these include antigens A and B, which determine the A, B, and O blood groups of individuals; and antigen D, which we refer to as the rhesus factor.

Rhesus incompatibility

Some individuals, depending on what was inherited from their parents, have rhesus antigens on their red blood cells while others don't. People who have the rhesus factor have the positive sign added to their blood group, while people who lack rhesus have the negative sign instead.

The possibility of rhesus incompatibility arises when a couple who plans to conceive do not have the same rhesus factors - one is positive while the other is negative. The problem arises in a situation where the man is rhesus-positive and the woman is rhesus-negative. If the foetus happens to take after the father's rhesus-positive status, this can threaten the foetus and may result in stillbirth.

How incompatibility occurs

Our bodies produce fighter or protective proteins called antibodies against whatever the body considers as foreign. In an ideal state, you will not produce antibodies against something that the body considers familiar. When an individual has the positive rhesus factor, the body recognises that rhesus as "self" and would not produce antibodies to fight against it. Conversely, when a person is rhesus-negative and a rhesus-positive blood type is introduced into their body either through blood transfusion or during pregnancy, their body would consider the introduced rhesus as a foreign body and therefore produce antibodies to fight against it.

This problem mostly occurs with women who are rhesus-negative and carrying a rhesus-positive baby. When this happens, the mother's system develops antibodies against anything rhesus in the baby's blood. In most cases, during that particular pregnancy, these antibodies are only formed but do not attack the baby. They remain stored in the mother's body waiting for subsequent pregnancies. This stage is called rhesus sensitization. If she gets pregnant again with another rhesus-positive foetus, the stored antibodies then come out to attack the foetus and cause problems. This keeps happening in subsequent pregnancies once the foetus is rhesus-positive and the attack tends to get worse with each pregnancy down the line.

Effects on pregnancy

The antibodies from the mother attack the foetus' red blood cells and cause severe foetal anaemia or shortage of red blood cells. This can result in