Rh disease can be prevented by passively immunizing an Rh− woman with an anti-Rh antibody preparation early during her first pregnancy and again shortly after the birth of her first child. The exogenous anti-Rh antibodies bind to the Rh antigen on any fetal RBCs that accessed the maternal circulation during birth, clearing them before they can interact with naïve anti-Rh B cells in the mother. Virtually no memory anti-Rh B cells are generated, so that if the fetus in the next pregnancy is Rh+, the risk of fetal damage is reduced. As insurance, Rh− women are given anti-Rh antibodies throughout and after subsequent pregnancies.