The blood type of a child is determined by the blood type of the parents, and it is possible for a type A and type B parent to have a type O child. Blood type refers to the type of antigens on the surface of red blood cells, white blood cells, platelets, and other blood components. In the abo blood group system, the blood group system is usually divided into four categories based on the presence or absence of a-antigens or b-antigens on the red blood cells: a-antigens, b-antigens, o-antigens, and ab-antigens. Parents with blood types a and b can have children with blood types a, b, o and ab, except that the probability of having a baby with blood type O is slightly lower. If you need to have your blood type checked, you can have a blood test done at your doctor’s office. Usually there is no requirement for fasting, but if you are having a blood biochemistry test done at the same time, it is recommended that you abstain from food and water after 12:00 p.m. on the night before the test.