Bart's hydrops fetalis is lethal because:
c. Hb Bart's cannot release oxygen to fetal tissues(Ref: Nelson's 20/e p 2349-2352, Ghai 8/e p 341)As Hb Bart's consists of 4y chains, which have very high oxygen affinity, it cannot release oxygen to fetal tissues.
Hb Bart's cannot bind oxygen
The excess a-globin form insoluble precipitates
Hb Bart's cannot release oxygen to fetal tissues
Microcytic red cells become trapped in the placental
C.V.S.