Each person’s blood is one of four major types: A, B, AB, or O. Blood types are determined by the types of antigens on the blood cells. Antigens are proteins on the surface of blood cells that can cause a response from the immune system. The Rh factor is a type of protein on the surface of red blood cells. Most people who have the Rh factor are Rh-positive. Those who do not have the Rh factor are Rh-negative.
As part of your antenatal care, you will have blood tests to find out your blood type. If your blood lacks the Rh antigen, it is called Rh-negative. If it has the antigen, it is called Rh-positive.
When the mother is Rh-negative and the father is Rh-positive, the fetus can inherit the Rh factor from the father. This makes the fetus Rh-positive too. Problems can arise when the fetus’s blood has the Rh factor and the mother’s blood does not.
If you are Rh-negative, you may develop antibodies to an Rh-positive baby. If a small amount of the baby’s blood mixes with your blood, which often happens, your body may respond as if it were allergic to the baby. Your body may make antibodies to the Rh antigens in the baby’s blood. This means you have become sensitised and your antibodies can cross the placenta and attack your baby’s blood. They break down the fetus’s red blood cells and produce anemia. This condition is called hemolytic disease or hemolytic anemia. It can become severe enough to cause serious illness, brain damage, or even death in the fetus or newborn.
What happens if antibodies develop?
Once a woman develops antibodies, RhIg treatment does not help. A mother who is Rh sensitised will be checked during her pregnancy to see if the fetus is developing the condition.
The baby may be delivered on time, followed by a blood transfusion for the baby that will replace the diseased blood cells with healthy blood.
For more severe cases, the baby may be delivered early or given transfusions while in the mother’s uterus.
Compiled using information from the following sources:
Mayo Clinic Complete Book of Pregnancy & Babys First Year. Johnson, Robert V., M.D., et al, Ch. 11.
Danforths Obstetrics and Gynaecology Ninth Ed. Scott, James R., et al, Ch. 18