Bart's hydrops fetalis is lethal because –: (A) Hb Bart's cannot bind oxygen, (B) The excess a – globin form insoluble precipitates, (C) Hb Bart's cannot release oxygen to fetal tissues, (D) Microcytic red cells become trapped in the placental
Answer is C. `In the foetus excess, gamma globin chains form tetramers (1Ib Barts) with such high affinity for oxygen that they deliver almost no oxygen to tissues' - Robbins

Clinically this condition manifests as hydrops fetalis and fetus shows features similar to those of erythroblastosis fetalis → Severe pallor, Generalized edema, Massive hepatosplenomegaly