A 32-year-old woman with a history of two previous pregnancies (both uncomplicated deliveries) presents to the antenatal clinic at 28 weeks of gestation. She is RhD-negative and her current partner is RhD-positive. Routine antenatal blood tests show: Hb 11.2 g/dL, indirect antiglobulin test (IAT) negative. She has no history of transfusion. What is the most appropriate management at this stage to prevent hemolytic disease of the newborn (HDN)?

Explanation

## RhD Sensitization Prevention in Pregnancy **Key Point:** For an unsensitized RhD-negative pregnant woman at 28 weeks, the standard antenatal anti-D prophylaxis is **500 IU (100 μg) intramuscularly at 28 weeks** — this is the WHO/ICMR-recommended regimen and the standard followed in Indian clinical practice and NEET PG examinations. ### Timing and Dosing of Anti-D Immunoglobulin (WHO/ICMR Guidelines) | Gestation | Dose | Route | Indication | | --- | --- | --- | --- | | 28 weeks | 500 IU | IM | Routine antenatal prophylaxis | | Delivery | 500 IU IM (+ extra if large FMH) | IM | Postpartum within 72 hours | | Sensitizing event | 250–500 IU | IM | Antepartum hemorrhage, amniocentesis, ECV, etc. | **High-Yield:** The single-dose regimen at 28 weeks (500 IU IM) is the standard recommendation per WHO and ICMR guidelines. The two-dose regimen (28 + 34 weeks) is specific to UK RCOG/NICE practice and is **not** the standard tested in Indian postgraduate examinations. ### Why This Patient Needs Prophylaxis 1. **RhD-negative status** with RhD-positive partner → risk of fetal RhD incompatibility 2. **Negative IAT** → currently unsensitized (no circulating anti-D antibodies) 3. **28 weeks gestation** → optimal timing for antenatal prophylaxis; fetal–maternal hemorrhage risk increases in the third trimester 4. **No prior transfusion history** → sensitization risk is from obstetric FMH only **Clinical Pearl:** Anti-D immunoglobulin works by clearing fetal RhD-positive red cells from the maternal circulation before they can trigger an immune response. The 28-week dose covers the period of highest FMH risk in the third trimester. (Reference: DC Dutta's Textbook of Obstetrics, 9th ed.; WHO guidelines on Rh prophylaxis) ### Why Not the Other Options? - **Option B (500 IU at 28 weeks + repeat at 34 weeks):** This two-dose regimen is specific to UK RCOG/NICE guidelines and is not the standard in Indian/WHO practice. For NEET PG purposes, the single 500 IU dose at 28 weeks is correct. - **Option C (100 IU/kg IV based on fetal weight):** Incorrect — prophylactic anti-D is given as a fixed dose (500 IU) intramuscularly, not intravenously and not weight-based. - **Option D (Amniocentesis + defer anti-D):** Amniocentesis is itself a sensitizing event requiring anti-D cover; deferring prophylaxis increases sensitization risk and is not indicated in an uncomplicated pregnancy with negative IAT.