A 28-year-old Rh-negative primigravida presents for routine prenatal care at 28 weeks of gestation. Maternal antibody screen (indirect Coombs test) is negative, indicating she is unsensitized. The father of the fetus is known to be Rh-positive. To prevent Rh (anti-D) alloimmunization, what is the standard prophylactic protocol?

Answer and explanation

Correct answer: C. Administer Anti-D Immune Globulin at 28 weeks, and repeat within 72 hours if neonate is Rh+

  1. Step 1: RhD alloimmunization occurs when an Rh-negative mother is exposed to Rh-positive fetal red cells, producing maternal IgG antibodies that can cross the placenta in subsequent pregnancies and cause hemolytic disease of the fetus and newborn (erythroblastosis fetalis).
  2. Step 2: In unsensitized Rh-negative women, standard prophylaxis involves administering 300 mcg (1,500 IU) of anti-D immune globulin at 28 weeks' gestation.
  3. Step 3: A second dose is administered postpartum within 72 hours if the neonate's blood type is confirmed Rh-positive. Additional doses are given after any fetomaternal hemorrhage event (e.g., trauma, amniocentesis).
Answer
Administer Anti-D Immune Globulin at 28 weeks, and repeat within 72 hours if neonate is Rh+.
Why not the others: 'Administer only after delivery' fails to prevent alloimmunization occurring from occult third-trimester fetomaternal bleeding; 'Corticosteroids' do not prevent Rh sensitization; 'No intervention unless Coombs becomes positive' is wrong because once anti-D antibodies develop, immune globulin is completely ineffective.

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