Question

The problem of erythroblastosis fetalis occurs when?

Answer 1

Hint: All people have a blood type (A, B, AB, or O). Everyone has Rh factor (positive or negative) and the problem occurs if mother and baby have different blood types and Rh factor which leads to destruction of RBCs.

Complete answer
Erythroblastosis fetalis is a condition that results from incompatibility between certain blood types of a woman who is pregnant and foetus.
 Main causes of erythroblastosis fetalis is Rh incompatibility and ABO incompatibility .both can be associated with blood type, if person has A positives blood then they have A and Rh antigen on the surface of blood cells and if person has AB negative blood then have A and B antigen without Rh antigen.
If a woman is Rh negative and foetus is Rh positive, it can lead to Rh incompatibility, then the Rh negative mother's immune system sees the baby's Rh positive blood cells as foreign cells, and the mother's immune system responds by making antibodies to fight with these foreign cells.
The immune system becomes Rh sensitized and stores antibodies for foreign cells but Rh sensitization isn’t a problem with a first pregnancy, problem occurs in future pregnancy with another Rh positive baby. During that pregnancy the mothers antibodies cross the placenta to fight the Rh positive cells of the baby, as antibodies destroy the RBCs of the baby .

Thus the problem of erythroblastosis fetalis occurs when father is Rh positive and mother is Rh negative.

Note:
If a mother is Rh negative and father is Rh positive, a baby may have Rh positive blood, inherited from the father but if both parents have Rh negative blood the baby will have Rh negative blood and this will not lead to any problem in pregnancy because both blood are matched with each other.