What determines a child's blood group?

Is croup contagious?

Why does my son become unconscious when he cries?

Question
What determines a child's blood group? And is it possible for children from the same partners to be of different groups?

Answer
The membranes of human red blood cells contain a variety of antigens, the most important of which are the A, B and O antigens.

People are divided into four major blood types: A, B, AB and O, depending on which antigens they have.

Every individual inherits one antigen from each of their parents and the A and B antigens are called the 'dominant' ones.

This means that if a person has one B and one O antigen the B will be dominant over the O and their blood reacts as type B.

It is quite possible for children to have a different blood type from their parents, even if both parents have the same blood type. For example, if both parents are type B and have the BO antigens, they could have children who are BB (B antigen inherited from both parents), BO (B from one parent, O from the other) or OO (O antigen from both parents).

This makes analysis of blood types sound very simple but if antigens other than those in the ABO system are looked at, the picture may become more complicated.

At least nine major and 24 minor antigen systems are now recognised so if these are also analysed it might show that individuals who have the same ABO blood type have numerous differences with regard to other antigens. I hope this answers your query!

Yours sincerely

The Medical Team