What happens when an O blood type person has a baby with an AB blood type person?

i believe O is recessive, so im pretty sure bloodtype will be AB.
look up punnett squares relating to human blood type. AB is dominant compared to O. thats why its rare that ppl are o.

There's a 50% chance that the baby will have blood type A, and 50% chance for type B.
There will be no O blood type though...and no AB!

Because you get one allele (version of the gene) form mom and the other from dad...If the mother is AB she will either give you a B allele or an A. The father is O (OO) so he'll give you an O no matter what. so you'll end up being either AO, or BO....which is actually blood type A or B.

There is a 50% chance the child will have type B blood (BO) and a 50% chance the child will have type A blood (AO).

For the sake of explanation let's say that the mother has type O blood and the father has type AB blood. Type O blood is the result of not having either A or B antigens and is therefore a recessive trait. Having type AB blood means that the father has both A and B antigens. The mother only has two of the same allele so no matter what she will give the baby an "O" allele. The father will give the baby either an A allele or a B allele. This means that the baby will either be AO or BO. Since "O" is a resessive trait the A or the B will be dominant resulting in the child having either type A blood (AO) or type B blood (BO).

When thinking about blood type and procreation the real concern is the Rh-antigen, such as O+, O-, A+, A-, B+, B-, etc. When someone has the Rh-antigen they are considered to be "+." If they don't have the Rh-antigen they are considered to be "-." Most problems with blood type compatibility occur if the mother is Rh-negative and the baby is Rh-positive. If a small amount of the baby's blood mixes with the mothers blood, the mother's body may respond to it as if it was an allergic reaction.The mother makes antibodies to the Rh antigens in the baby's blood which means that the mother's body can attack the baby resulting in the break down the fetus's red blood cells and producing anemia (the blood has a low number of red blood cells). This condition is called hemolytic disease or hemolytic anemia. It can become severe enough to cause serious illness, brain damage, or even death in the fetus or newborn.

This is why it is highly encouraged to know the blood type of both the father and the mother before conceiving so appropriate precautions can be taken to prevent this from happening.

What a question!
 I am sure sure if I can exactly answer it but I'm AB & my mother is O & my father is AB. I was also born 6 weeks premature & put in an incubator due to the "blood incompatibility"& they thought I might need a transfusion but I came out OK. Yay!