A 32-year-old multigravida, Rh-negative, presents at 32 weeks of gestation with vaginal bleeding (approximately 10 mL). Indirect Coombs test is negative. Her previous two pregnancies ended in normal vaginal delivery; she received anti-D prophylaxis postpartum after both. She has never received antenatal anti-D. What is the most appropriate immediate management?

Explanation

## Management of Sensitising Event in Rh-Negative Pregnancy ### Clinical Scenario This is an unsensitised (ICT-negative) Rh-negative woman at 32 weeks with **antepartum haemorrhage (APH)**, a classic sensitising event. The volume of bleeding (~10 mL) is small but warrants immediate anti-D prophylaxis and assessment for fetal–maternal haemorrhage (FMH). ### Correct Management: Administer Anti-D Immediately + Perform Kleihauer–Betke Test **High-Yield:** Per RCOG Green-top Guideline No. 22 (2011) and standard obstetric practice, the correct sequence is: 1. **Administer anti-D 500 IU IM immediately** (within 72 hours of the sensitising event — ideally within 1 hour). 2. **Perform Kleihauer–Betke (KB) test concurrently** to quantify FMH. 3. **If FMH ≥4 mL fetal red cells**, administer additional anti-D based on quantification (100 IU per mL fetal red cells above the threshold). Anti-D is **never withheld** pending the KB result — the test is used to determine whether *additional* anti-D is needed, not to decide whether to give the initial dose. ### Key Dosing Rules | FMH Volume | Initial Anti-D Dose | Additional Dose | |---|---|---| | <4 mL fetal RBCs | 500 IU IM | None | | ≥4 mL fetal RBCs | 500 IU IM | 100 IU per mL fetal RBCs above threshold | ### Why Option A is Correct - Administering **500 IU anti-D IM immediately** covers the standard FMH expected from a minor sensitising event. - Performing the **KB test concurrently** allows dose adjustment if FMH is unexpectedly large. - This is the standard RCOG/ACOG-recommended approach: give anti-D first (or simultaneously), then quantify. ### Why Option B is Incorrect Option B implies a **strictly sequential** approach — perform KB test *first*, then decide on anti-D. This is **not standard practice** and risks delay beyond the 72-hour window. The KB test is performed to guide *additional* dosing, not to gate the initial dose. The RCOG guideline explicitly states anti-D should be given promptly and KB performed to confirm adequacy. ### Why Other Options Are Incorrect - **Option C:** "100 IU/kg" is the dose used for large FMH (>4 mL fetal RBCs), not the standard initial dose for a minor sensitising event. Repeating ICT in 1 week is not the standard follow-up. - **Option D:** Anti-D must never be withheld pending ultrasound. Fetal viability and placental location are assessed separately; they do not alter the need for anti-D in an unsensitised Rh-negative woman with a sensitising event. **Clinical Pearl:** The Kleihauer–Betke test is a *dose-adjustment* tool, not a *decision-making* tool for whether to give anti-D. Always administer the standard 500 IU dose immediately, then adjust upward if KB reveals large FMH [RCOG Green-top Guideline No. 22, 2011; Williams Obstetrics, 25th ed.].