A Rh-negative primigravida at 28 weeks receives antenatal anti-D prophylaxis (300 µg IM). At 36 weeks, indirect Coombs test is weakly positive. The CORRECT interpretation is:

• A She has become alloimmunized and needs plasmapheresis
• B The fetus is at immediate risk of hemolytic disease and cordocentesis is indicated
• C Anti-D should not have been given at 28 weeks as it caused alloimmunization
• D This is residual antibody from antenatal prophylaxis — not true alloimmunization ✓

Explanation

Antenatal anti-D prophylaxis given at 28–32 weeks can produce a weakly positive indirect Coombs test (passive anti-D) that persists until delivery and does not represent active alloimmunization. This is a passive antibody from the injection, not an immune response. Titers from passive anti-D are typically low (≤1:4) and static. Rising titers, high titers (>1:16), or a titer becoming positive in a woman who was previously negative without prophylaxis would suggest true alloimmunization requiring further monitoring.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.