Under what parental combination can Rhesus incompatibility disease (erythroblastosis fetalis / hemolytic disease of the newborn) occur in a second or subsequent pregnancy?
Answer and explanation
Correct answer: A. Rh-negative mother carrying a second Rh-positive fetus conceived with an Rh-positive father
- Step 1: During a first delivery of an Rh-positive baby, fetal Rh-positive erythrocytes enter the Rh-negative mother's circulation, sensitizing her to produce anti-Rh antibodies (IgG). Step 2. In subsequent pregnancies with an Rh-positive fetus, maternal IgG antibodies cross the placenta and destroy fetal red blood cells. Answer: Rh-negative mother carrying a second Rh-positive fetus conceived with an Rh-positive father. Why not the others: Rh-positive mothers already have Rh antigen and don't make anti-Rh antibodies; if both parents are Rh-negative, all children are Rh-negative.
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