Question

multiple choice question
what causes hemolytic disease of the newborn?

maternal b antigens cause fetal production of anti - b antibodies.

fetal anti - d destroys maternal erythrocytes.

fetal anti - a destroys fetal erythrocytes.

maternal anti - d destroys fetal erythrocytes.

Explanation:

Hemolytic disease of the newborn (HDN) occurs when maternal antibodies attack fetal red blood cells. In cases involving Rh factor (D antigen), if a mother is Rh - negative and the fetus is Rh - positive, the mother can develop anti - D antibodies. These maternal anti - D antibodies can cross the placenta and destroy fetal (Rh - positive) erythrocytes.

• The first option is incorrect because maternal B antigens don't cause fetal anti - B production in a way that leads to HDN (ABO incompatibility has a different mechanism and is less severe, and this option's description is not the main cause of typical HDN).
• The second option is incorrect as fetal anti - D doesn't destroy maternal erythrocytes; it's the other way around (maternal antibodies attacking fetal cells).
• The third option is incorrect as fetal anti - A destroying fetal erythrocytes is not the cause of HDN (ABO HDN is milder and the mechanism is different, and this option misrepresents the direction of antibody action).
• The fourth option is correct as maternal anti - D (from Rh - negative mothers exposed to Rh - positive fetal blood) can cross the placenta and destroy fetal (Rh - positive) erythrocytes, causing HDN.

Answer:

D. Maternal anti - D destroys fetal erythrocytes. (Note: Assuming the options are labeled A, B, C, D in order. If the original options had different labels, adjust accordingly. Here, the fourth option is the correct one with the description "Maternal anti - D destroys fetal erythrocytes".)