This rarest of blood types is defined by an unusual Rh factor that is neither negative nor positive ... Specifically, this ...

Ounce of Prevention is a weekly column which presents recommendations for preventative services derived from The United ...

It's a bit simplistic, but you can think of the Rh factor as a protein that is either present (positive) or absent (negative) on red blood cells ... ones in RhoGAM are a type that won't cross ...