Aetiology

One of the most severe causes of this condition is rhesus incompatibility.

Other causes include, in descending order of frequency and severity:

• ABO system incompatibility
• red blood cell metabolic disorders - for example, G-6-PD deficiency, pyruvate kinase deficiency
• RBC morphology disorders - for example, hereditary spherocytosis, hereditary elliptocytosis

Rhesus incompatibility tends to be more severe than ABO incompatibility because anti-D antibodies are mainly IgG, which can readily cross the placenta, whereas anti-A and anti-B antibodies are mainly IgM, which cannot cross the placenta.