The Rh factor is a type of protein that's usually found on red blood cells. When you have this protein, you’re considered Rh positive. About 85% of people are Rh-positive. The rest are Rh-negative.

When a woman and her unborn baby carry different Rhesus (Rh) protein factors, their condition is called Rh incompatibility. It occurs when a woman is Rh-negative and her baby is Rh-positive. The Rh ...