A 32-year-old Rh-negative woman, G2P1, presents at 28 weeks of gestation with a positive indirect Coombs test (ICT) and antibody titre of 1:32 against anti-D. She has a history of transfusion with Rh-positive blood 5 years ago. Ultrasound shows no signs of fetal hydrops. What is the most appropriate next step in management?

Explanation

## Clinical Context This is an Rh-negative sensitised woman (positive ICT, titre 1:32) at 28 weeks with prior Rh-positive transfusion exposure. She is now pregnant and at risk of haemolytic disease of the fetus and newborn (HDFN). Ultrasound shows no hydrops yet, but fetal assessment is needed. ## Management Algorithm for Sensitised Pregnancy ```mermaid flowchart TD A[Rh-negative sensitised woman<br/>Positive ICT, Titre ≥1:8]:::outcome --> B{Signs of fetal hydrops<br/>on ultrasound?}:::decision B -->|Yes| C[Cordocentesis for fetal<br/>haemoglobin & bilirubin]:::action C --> D{Fetal anaemia<br/>severe?}:::decision D -->|Yes| E[Intrauterine transfusion<br/>or early delivery]:::action B -->|No| F[Amniocentesis for<br/>ΔOD450 bilirubin]:::action F --> G{ΔOD450 in<br/>high zone?}:::decision G -->|Yes| H[Cordocentesis for<br/>fetal Hb assessment]:::action G -->|No| I[Repeat amniocentesis<br/>in 1-2 weeks]:::action H --> J{Fetal Hb<br/>< 7 g/dL?}:::decision J -->|Yes| K[Intrauterine transfusion]:::action J -->|No| L[Deliver at 37-38 weeks<br/>or repeat testing]:::action ``` ## Why Amniocentesis First? **Key Point:** In a sensitised pregnancy WITHOUT signs of hydrops, amniocentesis is the first-line test to assess fetal haemolysis severity via amniotic fluid bilirubin (ΔOD450 value plotted on Liley chart). **High-Yield:** Liley chart zones: - **High zone:** Risk of severe fetal anaemia; proceed to cordocentesis ± intrauterine transfusion - **Mid zone:** Moderate risk; repeat amniocentesis in 1–2 weeks - **Low zone:** Low risk; repeat in 2–4 weeks or deliver at term **Clinical Pearl:** Cordocentesis is reserved for: 1. Hydrops already present (direct fetal assessment needed urgently) 2. ΔOD450 in high zone (to confirm severity and transfuse if needed) 3. Uncertainty after amniocentesis Cordocentesis carries 1–2% fetal loss risk and should not be first-line in non-hydropic fetuses. ## Staging of Haemolytic Disease | Stage | Ultrasound Findings | Management | | --- | --- | --- | | **Mild** | Normal, no ascites | Amniocentesis for ΔOD450 | | **Moderate** | Ascites, normal heart size | Amniocentesis; if high zone → cordocentesis | | **Severe (Hydrops)** | Ascites, cardiomegaly, pleural effusion, oedema | Cordocentesis ± IUT; early delivery | **Mnemonic: AMNIO FIRST** — **A**ssess fetal haemolysis, **M**easure ΔOD450, **N**o hydrops yet, **I**nvasive cordocentesis second-line, **O** — **F**irst-line non-hydropic, **I**ntrauterine transfusion if severe, **R**epeat if mid zone, **S**evere hydrops → cordocentesis, **T**ransfer for specialist care. ## Why NOT Anti-D Immunoglobulin? **Warning:** Anti-D is contraindicated in already-sensitised women (positive ICT). It will not prevent further sensitisation (already occurred) and may worsen haemolysis. Anti-D is only for unsensitised, Rh-negative women.