Hemolytic reaction does not usually occur in children born to a mother with blood type A and a father with blood type O. The mechanism of hemolytic reaction between blood type O and blood type A is an antigen-antibody reaction.
The mechanism of hemolytic reaction between blood type O and blood type A is antigen-antibody reaction. If the mother has type A blood and the father has type O blood, the child may be born with type A or type O blood. However, regardless of whether the child has type O or type A blood, it will not stimulate the mother to produce antibodies, so hemolytic reaction will not occur.
However, if the mother has type O blood and the father has type A blood, there is a partial chance that the child will have a hemolytic reaction. If the mother has type O blood and the child is born with type O blood, no hemolytic reaction will occur; however, if the child is born with type A blood, since type A blood contains A antigen, it can react with the anti-A antibody in type O blood, resulting in hemolysis.