·         Prenatal findings in complex congenital defects tend to underestimate the severity of the abnormalities.

·         Mild valve disease may be missed without Doppler because the valves ‘look normal’.

·         Blood flow velocities may be lower than after birth because of low ventricular pressures present in fetal life, e.g. lack of significant pressure difference across a VSD in utero means that flow through the VSD may not be demonstrable by Doppler.

·         Ultrasound resolution is 1—1.5 mm, thus may miss a small VSD.

·         Mild aortic coarctation/secundum ASD: are ‘normal variants’, in utero.

·         Changes during pregnancy: cardiomyopathies worsen in later weeks and VSD may close in later weeks.

·         Aortic isthmus narrowing is a normal feature in utero. It can be distinguished from coarctationbecause of lack of other recognized features, e.g. left/ ventricle is normal size not small.

·         In complex cardiac defects the main lesion may be recognizable but secondary lesions may be missed.



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