The influence of twinning on cardiac development.

The risk for a cardiac anomaly in a twin pregnancy is increased, particularly in monochorionic twins. This is relevant in terms of fetal diagnosis as well as for the management of the pregnancy; there are also implications for the neonatal period and possibly beyond. The risk for a cardiac abnormality depends on the type of monochorionic twin as determined by the timing of embryonic division. Prenatal identification of twin type and the relative risks for a cardiac anomaly are discussed along with theories for the aetiology of the different cardiac lesions.