Why treat "physiologic" anemias of pregnancy?

It is argued that the physiologic anemia of midpregnancy is beneficial in terms of the associated hypervolemia and improved pregnancy outcome. Vigorous treatment of normal pregnant women having physiologic anemias with large doses of medicinal iron is discouraged because higher hematocrits are reported to be less efficient in terms of cardiac work and oxygen delivery, because lower serum iron levels protect against infection and because of the hazards of infant iron poisoning. Pharmacologic doses of iron also obscure the decline in hematocrit seen from the plasma volume expansion in normal pregnancy, removing a simple diagnostic sign of maternal hypovolemia.