Alpha-thalassaemia is one of the most common human genetic disorders. Couples in which both partners carry alpha(0)-thalassaemia traits have a 25% risk of having a fetus affected by homozygous alpha-thalassaemia or haemoglobin Bart's disease, with severe fetal anaemia in utero, hydrops fetalis, stillbirth or early neonatal death, as well as causing various maternal morbidities. This disorder is common in southeast Asia and southern China, and the expanding populations of southeast Asian immigrants in the US, Canada, UK and Europe mean that this disorder is no longer rare in these countries.