A woman with type O blood and a man with type A blood may give birth to a child with hemolytic reaction.
This is because women with type O blood have anti-A and anti-B antibodies in their blood, and if they marry a man with type A blood, they may give birth to a child with type O or type A blood. If the child is born with type O blood, no hemolytic reaction will occur; if the child is born with type A blood, type A blood contains A antigen, which can react with anti-A antibody in type O blood, resulting in ABO hemolysis, leading to jaundice and so on.
Therefore, if a woman with type O blood is pregnant, it is better to check the antibody titer related to the blood type during the maternity checkup, and take measures to prevent hemolysis in the newborn according to the antibody potency.