If you’re pregnant and are being recommended the Rhogam shot, you may have questions about whether this procedure is necessary or safe. The Rhogam shot is often given to mothers with a negative blood type at 28 weeks and within 72 hours of birth. You probably remember how there are different blood types: A, B, AB and O. Sometimes you’ll hear blood types mentioned as A positive, or A negative. That negative or positive indicates your Rh factor. If a particular protein is present on your red blood cells, you’re Rh positive. If your blood type was B, they’d say you’re B positive—your blood is in the B group and you’re Rh positive. B negative would mean your blood is in the B group but you’re missing that special protein on your red blood cell. You’re RH negative. About 82% of people are Rh positive. Some are Rh negative. It doesn’t make you unhealthy or anything, but it can cause a problem under a very rare circumstance.