Anti-D immunoglobulin is given routinely at 28 weeks in an Rh-negative woman (antenatal anti-D prophylaxis). What is the primary rationale for this timing?

• A Spontaneous fetomaternal hemorrhage is most common in the third trimester
• B To suppress the fetal immune response before delivery
• C To prevent anti-D from crossing the placenta and causing hemolysis
• D To prevent sensitization from silent fetomaternal hemorrhage occurring in the third trimester before any sensitizing event ✓

Explanation

Routine antenatal anti-D prophylaxis at 28 weeks (and sometimes 34 weeks) is given to prevent sensitization from unpredictable, clinically silent transplacental fetal-to-maternal red cell passage, which increases in frequency and volume during the third trimester. It covers the period between sensitizing events (e.g., amniocentesis or trauma) and delivery. The 28-week dose does not provide permanent protection and a postnatal dose must still be given after delivery of an Rh-positive infant.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.