The purpose of this non-interventional study is to prospectively evaluate the risk of anemia (decreased red blood cells) in fetuses (baby before birth) and neonates (baby just after birth) of pregnant participants who are at risk for hemolytic disease of the fetus and newborn (HDFN) and receiving standard of care (SoC). HDFN is a blood disease that occurs in babies before birth or just after birth when the blood types of the pregnant individual and babies are incompatible, thus resulting in fast breakdown of red blood cells (RBCs) of the fetus/baby.