Blood Types

Blood Tubes

Every pregnant woman has her blood type checked. It is part of regular prenatal care. When your baby is born, he may or may not have his blood type checked. Whether he gets her blood type checked depends on Mom's blood type.

Our blood type refers to the kinds of proteins that occur on the surface of our red blood cells (RBCs). The possible blood types are: O+, O-, A+, A-, B+, B-, AB+ and AB-. O+ is the most common blood type. AB- is the rarest blood type.

The babies of moms with negative blood types, O-, A-, B-, and AB-, automatically get their blood type checked. There is a condition called RH incompatibility, where mom has a (-) blood type and her baby has a (+) blood type. If Mom gets exposed to the baby's foreign blood protein during pregnancy, her immune system will make antibodies against the (+) protein. With each pregnancy, the amount of maternal antibody increases and the risk of harming the baby increases. When a severe RH incompatibility develops, the baby could develop a life threatening anemia before he is even born. By giving a shot, called RhoGam, to moms with (-) blood type during each pregnancy and again when each baby is born, the risk of damage to the baby's red blood cells can be prevented. If the baby also has (-) blood type, then there is no exposure to mom from foreign protein and RhoGam is not needed.

Blood Cells

The other situation is if mom has O type blood. The same thing can happen as with the (-) and (+) blood type difference, but it is not as severe. If mom has O+ or O- blood type, and the baby has A+, A-, B+, B-, AB-, or AB- blood type, an ABO incompatibility can develop. Mom's immune system may recognize the A or B proteins as foreign protein and make antibodies against the baby's red blood cells. The reason this is important is that yellow jaundice can be more severe in the baby. When the baby's blood type is checked, another test, called a DAT (or Coombs) test, can detect whether or not there are maternal antibodies in the baby's circulation. If the Coombs test is positive, then yellow jaundice is more likely to be a problem.

Thanks to Janelle Aby MD, Stanford School Of Medicine, Newborn Nursery, and Lucille Packard Children's Hospital for the use of occasional photographs.