Parents' genetics determine baby's blood type

November 19, 2013 

Q: If my blood type is A, and my husband's blood type is B, what will our baby's blood type be?

A: Your baby can have A, B, AB or O type blood. It is like your baby won the lottery of blood types. The discovery that there are blood "types" is credited to an Austrian, Karl Landsteiner.

For centuries giving a sick person a blood transfusion was pretty much a hit or miss situation. Some people got better quickly after the transfusion and others died. It was a risky to receive a blood transfusion. Karl Landsteiner began his testing of blood components around 1901. He discovered that when the bloods of different people were mixed together a phenomenon of clumping occurred. This led him to start experiments to identify what caused the clumping. He discovered that an immunological reaction, clumping, occurs when differing protein molecules compete against each other.

Our blood type is determined by the genes of our parents. Just like the color of our eyes. The differences amongst blood types are due to the presence or absence of certain protein molecules called antigens and antibodies. Antigens are on the surface of the red blood cells and antibodies are in the blood plasma. Antibodies are proteins that are secreted as a result of an antigen.

If you have type A blood you have A antigens on the surface of your red blood cells and B antibodies in your blood plasma. Type B blood has B antigens on the surface of the red blood cells and A antibodies in the plasma. People with AB blood have A and B antigens on the surface of their red blood cells, but have no A or B antibodies in their plasma. Type O blood has neither A or B antigens on the surface of the red blood cells but have both A and B antibodies in the plasma. There is another antigen that is referred to as the Rh factor. It is named after the Rhesus monkey. It is probably the next most important factor in knowing one's blood type. People that are Rh positive have the D antigen. That is another column someday.

Back to why your baby can possibly be A, B, AB or O blood type. Both you and your husband contribute equally to your baby's genetic pool. You have A antigens on the surface and B antibodies in your plasma. Your husband has B antigens on the surface of his red blood cells and A antibodies in his plasma. So any possibility of that combination is possible. If your husband was O, your baby could be A or O. If your husband was AB your child could be A, B or AB blood type. If both you and your husband were O, then your baby could only be O blood type. That is the only time when it is easy to predict what the blood type of a baby will be, when both parents are O.

When your baby is born blood will be sent to the lab to determine what your baby's blood type is. May you have a safe and happy delivery.

Katie Powers, R.N., is a board-certified lactation consultant and perinatal educator at Manatee Memorial Hospital's Family BirthPlace. Her column appears every other week in Healthy Living. Contact her at

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