An Rh-negative (D-negative) woman at 28 weeks gestation with Rh-negative partner and indirect Coombs test (ICT) negative receives routine antenatal anti-D prophylaxis. The dose of Rh immunoglobulin given at 28 weeks in India/UK guidelines and the half-life of anti-D immunoglobulin respectively are:

• A 300 mcg (1500 IU); half-life 12 weeks
• B 300 mcg (1500 IU); half-life 4 weeks
• C 250 IU (50 mcg); half-life 6–8 weeks; no booster required
• D 1500 IU (300 mcg); half-life 3 weeks with booster dose at 34 weeks ✓

Explanation

Anti-D immunoglobulin 1500 IU (300 mcg) given at 28 weeks has a half-life of approximately 21–28 days (3–4 weeks). UK NICE and RCOG guidelines recommend routine antenatal anti-D prophylaxis (RAADP) with 1500 IU at 28–30 weeks (single dose) or 500 IU at 28 and 34 weeks (two-dose regimen). The 3-week half-life means that by 34 weeks, levels may be falling, justifying a booster dose in the two-dose protocol. A positive ICT at 28 weeks from the prophylactic anti-D injection is expected and does not indicate sensitization. The 500 IU dose covers routine obstetric interventions (amniocentesis, external cephalic version) up to 20 mL of fetal blood.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.