Erythroblastosis fetalis typically occurs under which of the following maternal and fetal Rh factor combinations?

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Mother is Rh-negative and fetus is Rh-negativeMother is Rh-negative and fetus is Rh-positiveMother is Rh-positive and fetus is Rh-negativeMother is Rh-positive and fetus is Rh-positiveMother and fetus both have unknown Rh status

Explanation

Erythroblastosis fetalis arises when an Rh-negative mother carries an Rh-positive fetus. The mother's immune system may produce antibodies against the fetal red blood cells, leading to hemolytic disease of the newborn. This condition does not occur if both mother and fetus share the same Rh status.