Haemolytic disease of the newborn is an immune condition which develops after a rhesus negative mother becomes sensitised to the rhesus positive blood cells of her baby whilst in utero.

Haemolytic disease commonly occurs due to a mother who is blood group O and a baby who is group A, however this incompatibility is usually mild and exchange transfusion is rarely needed

HDN due to rhesus incompatibility is less common in developed in countries following the introduction of anti-D prophylaxis

Sensitisation event

“Sensitisation” events are events which cause foetal blood to cross the placenta into the maternal circulation and thus these are indications for anti-D prophylaxis.

these events usually occur at the time of delivery so first pregnancies are rarely affected

Examples of sensitisation events include:

• Antepartum haemorrhage
• Placental abruption
• Abdominal trauma
• External cephalic version
• Invasive uterine procedures such as amniocentesis and chorionic villus sampling
• Rhesus positive blood transfusion to a rhesus negative woman
• Intrauterine death, miscarriage or termination
• Ectopic pregnancy
• Delivery (normal, instrumental or caesarean section)

Features of haemolytic disease of the newborn

• Hydrops foetalis appearing as foetal oedema in at least two compartments (for example pericardial effusion, pleural effusion, ascites), seen on antenatal ultrasound