Sources of Error in Fetal Echocardiography
· 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.