A 28-year-old primigravida with Rh-negative blood group presents at 32 weeks of gestation for routine antenatal care. Her husband is Rh-positive. Indirect Coombs test (ICT) is negative. She has no history of transfusion or sensitizing events. What is the most appropriate management regarding Rh isoimmunisation prevention at this stage?

Explanation

## Antenatal Anti-D Prophylaxis in Rh-Negative Pregnancy ### Standard Dosing Schedule (Indian/Commonwealth Protocol) **Key Point:** For an unsensitized Rh-negative woman, the standard antenatal anti-D prophylaxis per Indian (FOGSI) and UK (RCOG) guidelines is **500 IU intramuscularly at 28 weeks, with a repeat dose at 34 weeks**. **High-Yield:** The two-dose antenatal regimen used in India and most Commonwealth countries: - **500 IU IM at 28 weeks** — covers the period of rising fetal-maternal hemorrhage (FMH) risk - **500 IU IM at 34 weeks** — provides continued passive protection through the remainder of pregnancy and delivery This is the regimen described in **Option D**, making it the most appropriate answer for this clinical scenario. ### Why Not the Other Options? | Option | Why Incorrect | |--------|--------------| | **A — 100 IU/kg IM** | Weight-based dosing is not the standard fixed-dose protocol used in India; 100 IU/kg ≈ 500–600 IU but is not the recommended regimen phrasing, and critically, it omits the 34-week repeat dose | | **B — Defer until after delivery + Kleihauer-Betke** | Kleihauer-Betke is used *after* delivery to quantify FMH and determine if additional anti-D is needed; deferring antenatal prophylaxis entirely is incorrect and dangerous | | **C — 500 IU IV single dose** | Intravenous route is not standard for anti-D prophylaxis; IM is the recommended route. A single dose without the 34-week repeat is also incomplete per standard protocol | ### Mechanism of Action Anti-D immunoglobulin (passive IgG antibodies) binds to fetal D-positive RBCs that enter maternal circulation, opsonizing them for rapid clearance before maternal B-lymphocytes can mount a primary immune response to the D antigen. ### Key Conditions for Administration | Criterion | Requirement | |-----------|-------------| | **Rh status** | Rh-negative (D-negative) mother | | **ICT result** | Negative (unsensitized) — if ICT positive, anti-D is futile | | **Timing** | 28 weeks + 34 weeks (two-dose regimen) | | **Route** | Intramuscular | | **Dose** | 500 IU per dose | ### Clinical Pearl Per **FOGSI guidelines** and **RCOG Green-top Guideline No. 22**, routine antenatal anti-D prophylaxis (RAADP) consists of two doses of 500 IU IM at 28 and 34 weeks, OR a single large dose of 1500 IU at 28–30 weeks (single-dose regimen used in some centers). The two-dose 500 IU regimen is the most widely tested and practiced in Indian postgraduate examinations. **Reference:** Dutta DC, *Textbook of Obstetrics*, 9th ed.; RCOG Green-top Guideline No. 22 (2011); FOGSI Good Clinical Practice Recommendations on Rh Isoimmunisation.