A 28-year-old primigravida with Rh-negative blood group presents at 34 weeks of gestation for routine antenatal care. She has no history of transfusion or sensitization. Her indirect Coombs test (IAT) is negative. On examination, the fetus is in cephalic presentation with an estimated fetal weight of 2.2 kg. Her husband's blood group is O positive. What is the most appropriate management regarding Rh prophylaxis at this stage?

Explanation

## Rh Prophylaxis in Unsensitized Rh-Negative Primigravida at 34 Weeks **Key Point:** An unsensitized (IAT-negative) Rh-negative primigravida presenting at 34 weeks requires anti-D prophylaxis. The standard dose used in India (as per FOGSI/RCOG guidelines for routine antenatal prophylaxis) is **100 IU (20 µg) anti-D IM as a single dose** at this stage. ### Standard Antenatal Anti-D Prophylaxis Schedule (Indian/FOGSI Guidelines) | Gestation | Dose | Route | Notes | |-----------|------|-------|-------| | 28 weeks | 100 IU (20 µg) | IM | First antenatal dose | | 34 weeks | 100 IU (20 µg) | IM | Second antenatal dose | | Delivery | 300 IU (60 µg) or as per Kleihauer–Betke | IM | Within 72 hours of delivery | **High-Yield:** In the Indian context (FOGSI guidelines), the standard antenatal prophylaxis dose is **100 IU anti-D** given at 28 weeks and again at 34 weeks. This differs from the RCOG/UK protocol which uses 500 IU (100 µg). For NEET PG/INI-CET, the 100 IU dose at 28 and 34 weeks is the standard taught in Indian textbooks (Dutta's Obstetrics). ### Why Option A (100 IU anti-D IM as a single dose) is Correct - **Negative IAT** confirms she is unsensitized — anti-D prophylaxis is appropriate and safe - **34 weeks gestation** is the standard timing for the second antenatal prophylactic dose - **100 IU** is the correct dose per Indian (FOGSI) guidelines for routine antenatal prophylaxis - No need for amniocentesis (Option B) — that is reserved for sensitized patients to assess fetal hemolysis - Option C (500 IU and repeat at 36 weeks) is incorrect: 500 IU is the RCOG dose, and repeating at 36 weeks is not standard protocol - Option D is incorrect: 34 weeks is preterm, not term; withholding prophylaxis would leave the patient unprotected **Clinical Pearl:** Anti-D prophylaxis is given **regardless of fetal blood group** because fetal Rh status cannot be reliably determined without invasive testing. Since the husband is Rh-positive, the fetus has a significant probability of being Rh-positive, making prophylaxis essential. **Reference:** Dutta's Obstetrics, 9th edition; FOGSI guidelines on Rh isoimmunization prophylaxis — antenatal doses of 100 IU at 28 and 34 weeks for unsensitized Rh-negative mothers.