<prompt> Hydrops fetalis dt Hb ba is associated with?Hb bas cannot bind oxygenThe excess alpha-globin form insoluble precipitatesHb bas cannot release oxygen to fetal tissuesMicrocytic red cells become tapped in the placenta  <response>: - Hydrops fetalis is seen in most severe form of a-thalassemia, caused by deletion of all four a-globin genes. - Hb in these fetus have tetramers of g-globin chains hemoglobin Bas which have high affinity for oxygen. - This results in decreased delivery of oxygen to the tissues. - Survival in early development of these fetus is dt expression of z chains, an embryonic globin that pairs with g chains to form functional z 2 g 2 Hb tetramer. 