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MBBS QUESTION #10227
Question 1
An Rh-negative mother who is pregnant with an Rh-positive fetus is generally not at significant risk during her first pregnancy, but subsequent Rh-positive pregnancies carry a risk of hemolytic disease of the newborn. This is best explained by:
  • Maternal anti-Rh IgM formed during the first pregnancy freely crossing the placenta in later pregnancies
  • Maternal sensitization during the first pregnancy/delivery producing anti-Rh IgG antibodies, which can cross the placenta in subsequent pregnancies and hemolyze fetal RBCs✔️
  • The fetus producing antibodies against maternal red cells
  • ABO incompatibility being the sole mechanism, unrelated to Rh status
Correct Answer Explanation
Exposure to fetal Rh-positive red cells (typically at delivery) sensitizes the Rh-negative mother, who mounts an IgG antibody response. Because IgG (unlike IgM) crosses the placenta, subsequent Rh-positive pregnancies are at risk of antibody-mediated fetal hemolysis — the rationale for anti-D immunoglobulin prophylaxis after each Rh-positive delivery or sensitizing event.