There are two main causes of erythroblastosis fetalis:Rh incompatibilityandABO incompatibility.

Both causes are associated withblood type. There are four blood types:

A

B

AB

O

In addition, blood can be either Rh positive or Rh negative.

For example, if you’re type A and Rh positive, you have A antigens and Rh factor antigens on the surface of your RBCs. Antigens are substances that trigger an immune response in your body.

If you have AB negative blood, then you have both A and B antigens without the Rh factor antigen.

Rh incompatibility

Rh incompatibility occurs when a Rh-negative mother is impregnated by a Rh-positive father. The result can be a Rh-positive baby.

In such a case, your baby’s Rh antigens will be perceived as foreign invaders, the way viruses or bacteria are perceived. Your blood cells attack the baby’s as a protective mechanism that can end up harming the child.

If you’re pregnant with your first baby, Rh incompatibility isn’t as much of a concern.

However, when the Rh-positive child is born, your body will create antibodies against the Rh factor. These antibodies will attack the blood cells if you ever become pregnant with another Rh-positive baby.

ABO incompatibility

Another type of blood type mismatch that can cause maternal antibodies against her baby’s blood cells is ABO incompatibility. This occurs when the mother’s blood type of A, B, or O isn’t compatible with the baby’s.

This condition is almost always less harmful or threatening to the baby than Rh incompatibility. However, babies can carry rare antigens that can put them at risk for erythroblastosis fetalis.

These antigens include:

Kell

Duffy

Kidd

Lutheran

Diego

Xg

P

Ee

Cc

MNSs