Disorders of laterality and heterotaxy in the foetus

Disorders of laterality and heterotaxy syndromes are rare diseases with an incidence of 1-1.5/10,000 live births. They are associated with numerous viscerocardiac anomalies and malformations. In particular, heterotaxy syndromes are associated with complex cardiac and extracardiac malformations that have an important impact on the prenatal and postnatal course. A prenatal differentiation between the 2 main variants of heterotaxy--left and right isomerism--is possible by assessment of cardiac rhythm, anomalies of caval veins and descending aorta and concomittant cardiac and extracardiac anomalies. An exact diagnosis is mandatory for adequate counselling of the parents and planning of postnatal care. Left isomerism has a high intrauterine mortality, caused by early atrioventricular block with subsequent cardiac failure and hydrops. In contrast, right isomerism has a high postnatal mortality due to the more complex type of cardiac defects and splenic disorders. The type of associated cardiac and extracardiac anomalies determines the postnatal morbidity and mortality. Polysplenia and asplenia may be associated with immunological disorders, that cannot be ruled out in the prenatal period, and further complicate the postnatal course.