An Rh-negative woman at 32 weeks gestation with a positive indirect Coombs test and evidence of Rh sensitization presents with signs of fetal hemolytic disease. Intrauterine transfusion is planned. Which agent is the drug of choice to reduce hemolysis and improve fetal survival in this scenario?

Explanation

## Management of Established Rh Isoimmunisation **Key Point:** Once Rh sensitization is established (positive indirect Coombs test with rising titers), anti-D prophylaxis is ineffective. IVIG becomes the pharmacological agent of choice to reduce hemolysis and improve fetal outcome. ### Pathophysiology of Rh Isoimmunisation ```mermaid flowchart TD A[Rh-negative mother exposed to Rh+ fetal RBCs]:::outcome --> B[Primary immune response]:::outcome B --> C[IgM antibodies form]:::outcome C --> D[Secondary sensitization on re-exposure]:::outcome D --> E[IgG anti-D antibodies]:::outcome E --> F[Transplacental passage of IgG]:::outcome F --> G[Fetal RBC hemolysis]:::urgent G --> H{Severity?}:::decision H -->|Mild-moderate| I[IVIG + monitoring]:::action H -->|Severe| J[Intrauterine transfusion ± IVIG]:::action ``` ### Role of IVIG in Sensitized Pregnancies | Agent | Mechanism | Indication | Efficacy | |-------|-----------|-----------|----------| | **IVIG** | Blocks Fc receptors on macrophages; reduces RBC destruction | Established sensitization with fetal hemolytic disease | 40–60% reduction in hemolysis | | Anti-D | Coats fetal RBCs; prevents sensitization | Unsensitized Rh-negative women (prophylaxis) | Ineffective once sensitized | | Corticosteroids | Immunosuppression | Adjunct in severe cases | Limited evidence | | Plasma exchange | Removes maternal IgG antibodies | Severe sensitization; rarely used | Temporary effect only | **High-Yield:** IVIG at **2 g/kg daily** (or 1 g/kg on alternate days) is the first-line pharmacological agent for managing established Rh isoimmunisation with fetal hemolytic disease. ### Mechanism of IVIG in Hemolytic Disease 1. **Fc receptor blockade:** IVIG saturates Fc receptors on fetal macrophages and splenic reticuloendothelial cells 2. **Reduced opsonization:** Maternal IgG anti-D cannot effectively bind to fetal RBCs 3. **Decreased RBC destruction:** Fewer RBCs are hemolyzed; fetal anemia is mitigated 4. **Improved fetal survival:** Allows time for maturity or intrauterine transfusion **Clinical Pearl:** IVIG is most effective when started early in the course of fetal hemolytic disease (before severe anemia develops). It buys time for fetal maturity and reduces the need for or frequency of intrauterine transfusions. **Mnemonic:** **IVIG for Isoimmunised** — IVIG (not anti-D) is the drug of choice once Rh sensitization is confirmed. ### Adjunctive and Definitive Measures - **Intrauterine transfusion (IUT):** Transfusion of O Rh-negative, CMV-negative packed RBCs into fetal peritoneal cavity or umbilical vein; definitive treatment for severe fetal anemia - **IVIG + IUT:** Combined approach for severe disease; IVIG reduces hemolysis between transfusions - **Delivery:** Once fetal maturity is achieved (≥ 35 weeks), delivery and neonatal management (phototherapy, exchange transfusion) are preferred **Warning:** Anti-D immunoglobulin is contraindicated in sensitized women because the mother already has high-titer IgG anti-D antibodies; additional anti-D would not prevent hemolysis and may worsen the immune response.