A 24-year-old primigravida at 28 weeks of gestation presents for routine prenatal screening. Her blood type is A-negative with a negative indirect Coombs test (antibody screen). The father of the baby is known to be Rh(D)-positive. What is the recommended management to prevent Rhesus isoimmunization?

Answer and explanation

Correct answer: C. Administer 300 mcg (1,500 IU) of anti-D immune globulin intramuscularly at 28 weeks

  1. Step 1: Rhesus (Rh) isoimmunization occurs when an Rh(D)-negative mother is exposed to Rh(D)-positive fetal erythrocytes, producing maternal anti-Rh antibodies that cause hemolytic disease of the fetus/newborn in subsequent gestations.
  2. Step 2: Standard clinical practice guidelines recommend administering 300 mcg of anti-D immune globulin (RhoGAM) prophylactically to all non-sensitized Rh-negative pregnant women at 28 weeks of gestation, followed by a second dose within 72 hours of delivery if the newborn is confirmed Rh(D)-positive.
  3. Step 3: Anti-D is also given after any potential fetomaternal hemorrhage event (miscarriage, amniocentesis, trauma).
Answer
Administer 300 mcg (1,500 IU) of anti-D immune globulin intramuscularly at 28 weeks.
Why not the others: 'Withhold anti-D immunoglobulin until antibodies become positive' is incorrect because anti-D is ineffective once maternal sensitization has already occurred; 'Administer weekly IVIG' is unnecessary and inappropriate for routine prophylaxis; 'Perform immediate amniocentesis' is an invasive procedure that actually increases fetomaternal hemorrhage risk.

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