A 28-year-old primigravida with Rh-negative blood group presents at 34 weeks of gestation for routine antenatal checkup. She has no history of transfusion or sensitization. On examination, the uterus is appropriately sized. Indirect Coombs test (ICT) is negative. Her husband is Rh-positive. What is the most appropriate management regarding Rh prophylaxis at this stage?

Explanation

## Rh Isoimmunisation Prophylaxis in Unsensitized Rh-Negative Pregnant Women ### Antenatal Anti-D Prophylaxis Protocol **Key Point:** Unsensitized Rh-negative women (negative ICT) require antenatal anti-D immunoglobulin prophylaxis during pregnancy. The standard Indian (FOGSI) and international protocol recommends **500 IU (100 μg) intramuscularly** at 28 weeks and again at 34 weeks of gestation. ### Dosing Schedule (FOGSI / Williams Obstetrics) | Gestational Age | Dose | Route | |---|---|---| | 28 weeks | 500 IU (100 μg) | Intramuscular | | 34 weeks | 500 IU (100 μg) | Intramuscular | | Within 72 hours of delivery | 300 μg (1500 IU) or as per Kleihauer-Betke | Intramuscular | **High-Yield:** The standard antenatal prophylaxis dose is **500 IU administered intramuscularly**. The IM route is the universally accepted and recommended route in Indian guidelines (FOGSI) and standard obstetric textbooks (Williams Obstetrics, Dutta's Obstetrics). IV administration is NOT the standard or preferred route for anti-D immunoglobulin in routine antenatal prophylaxis. ### Clinical Scenario Analysis This patient is: - Primigravida (first pregnancy — no prior sensitization risk) - Rh-negative with Rh-positive partner (risk of fetal Rh incompatibility) - At 34 weeks (second dose of routine antenatal prophylaxis) - Negative ICT (not yet sensitized — prophylaxis is appropriate) **Clinical Pearl:** Anti-D prophylaxis is indicated at 34 weeks in this unsensitized Rh-negative woman. Deferring until after delivery (Option A) is incorrect because antenatal sensitization can occur during the third trimester. The correct dose is 500 IU IM (Option B), not IV. ### Why NOT IV Route? 1. Anti-D immunoglobulin is formulated and licensed for **intramuscular** administration in routine prophylaxis 2. FOGSI, RCOG (2011 Green-top Guideline No. 22), and Williams Obstetrics all specify IM as the standard route 3. IV anti-D is reserved for specific situations (e.g., patients with bleeding disorders where IM is contraindicated), not routine antenatal prophylaxis 4. Option D (500 IU IV) and Option C (100 IU IV) both use an incorrect route for routine prophylaxis **Mnemonic:** **ANTI-D at 28 & 34 — 500 IU IM** — Two standard intramuscular doses at these gestational ages in unsensitized Rh-negative women. [cite: Williams Obstetrics 25e Ch 5; Dutta's Obstetrics 9e; FOGSI Guidelines on Rh Isoimmunisation]