A baby born from the combination of male blood type O and female blood type A does not usually result in hemolysis. Hemolysis caused by mother-child blood type incompatibility means that the antibodies in the mother’s body do not match the antigens of the fetus’s blood type, and the mother’s antibodies can enter the fetus’s body through the placenta, causing immune hemolysis. In the case of a male with blood type O and a female with blood type a, the baby may be type O or A. The baby’s antigens will not react with the mother’s antibodies. However, if the mother’s blood type is RH-negative and she has a history of previous pregnancies, she may have special antibodies in her body, resulting in an increased chance of hemolysis in the baby, which may be of a very serious degree. This is why it is not only necessary to check the ABO blood group system but also the RH blood group when a woman becomes pregnant.