Why are fetuses in successive pregnancies of a sensitized Rh-negative mother typically affected more severely than the index affected child?

• A Maternal IgM antibodies cross the placenta more efficiently in later pregnancies
• B Fetal liver immaturity worsens with each successive pregnancy
• C The placenta becomes thinner with advancing parity, allowing larger red cell leaks
• D Repeat antigen exposure triggers an anamnestic response producing higher titres of placenta-crossing IgG ✓

Explanation

Once sensitized, memory D cells respond to even tiny transplacental bleeds in subsequent pregnancies with a rapid secondary immune response. This produces high titred IgG anti-B, which crosses the placenta via Fc receptors and causes progressive haemolysis. IgM does not cross the placenta, which eliminates option A. Fetal hepatic erythropoiesis capacity determines severity within a given pregnancy but does not deteriorate across pregnancies independently of antibody titre.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.