The blood types of children born from parents with type A and AB are generally type A, B and AB. Blood types are hereditary, and there are recessive and dominant genes for blood types, and blood types have a certain inheritance pattern. When a woman is pregnant, she can have her fetus’ blood type detected by amniocentesis. This test is mostly used for paternity testing or for blood disorders, and parents who are anxious to know their child’s blood type can have such tests performed during pregnancy to clarify the blood type. If you choose to have this test, it is best to have it around the 4th to 5th month of pregnancy when the amount of amniotic fluid is most abundant and less likely to harm the fetus.