Haemolytic disease of the fetus and newborn — branching viva

Branch 1 — Mechanism and prevention

The examiner opens: "Explain how this woman became sensitised and how it could have been prevented." A strong candidate traces the fetomaternal haemorrhage that exposed her to fetal RhD-positive cells, the maternal immune response producing anti-D IgG, and the fact that this crosses the placenta from about 16 weeks via the neonatal Fc receptor to bind and destroy fetal red cells. The prevention is antenatal and postnatal anti-D immunoglobulin to Rh-negative mothers, which suppresses sensitisation, and anti-D after any sensitising event such as a miscarriage — the Crowther Cochrane reviews established the evidence base. ^[1]