How does your blood type affect your pregnancy?

You’ve probably heard about the four main blood type classifications in humans: 

A       B     AB     O

In addition to these four main groups, people’s blood types can be further sub-categorized as being positive (+) or negative (-). What that refers to is the presence or absence of something called the Rh (Rhesus) Factor: a protein, or antigen, that is present on your red blood cells.

If your blood type is categorized as Rh-positive, you have the protein and RhD antigen. If your blood type is categorized as Rh-negative, you do not have the protein nor the RhD antigen. This distinction most matters when you are Rh-negative and your baby is Rh-positive.

Why does it matter? 

A problem is more likely to occur in people who are Rh-negative (you have a negative (-) sign after your blood type), which certain ethnic populations are more likely to be. To give you a quick...