If you just found out you're pregnant, one of the first - and
most important - tests you should expect is a blood-type test.
This basic test determines your blood type and Rh factor. Your
Rh factor may play a role in your baby's health, so it's
important to know this information early in your pregnancy.
About the Rh Factor People with different blood types have
proteins specific to that blood type on the surfaces of their
red blood cells (RBCs). There are four blood types - A, B, AB,
and O. Each of the four blood types is additionally classified
according to the presence of another protein on the surface of
RBCs that indicates the Rh factor. If you carry this protein,
you are Rh positive. If you don't carry the protein, you are Rh
Most people - about 85% - are Rh positive. But if a woman who is
Rh negative and a man who is Rh positive conceive a baby, there
is the potential for a baby to have a health problem. The baby
growing inside the Rh-negative mother may have Rh-positive
blood, inherited from the father