<prompt> Bas hydrops fetalis is lethal because:Hb Bas cannot bind oxygenThe excess a-globin form insoluble precipitatesHb Bas cannot release oxygen to fetal tissuesMicrocytic red cells become trapped in the placental  <response>: Hb Ba: Most severe form of Alpha thalassemia As Hb Bas consists of 4-gamma chains - have very high oxygen affinity Thus, it cannot release oxygen to fetal tissues. 