Echocardiographic evaluation of cardiac function in the fetus

The development of high-resolution ultrasound has allowed detailed examination of the fetal heart. The accuracy of fetal echocardiography in the diagnosis of malformations of the fetal heart has been established in the second trimester and, more recently, at a much earlier stage in gestation (Allan et al., 1980; Allan et al., 1981; Simpson, 2000; Huggon et al., 2002). Confirmation of structural abnormalities has usually been by autopsy or by postnatal investigation. This is certainly sufficient for confirmation of structural malformations, but functional evaluation of the fetal heart is far more difficult to validate. Post-mortem studies, by their very nature give little insight into cardiac function and postnatal studies, whilst permitting functional evaluation of the heart, do so under entirely different conditions compared to the circulation in utero. Prior to the advent of ultrasound, fetal data was drawn from invasive animal studies (Pohlman, 1909; Dawes et al., 1954; Barcroft, 1936; Rudolph, 1985). There have been very few invasive studies in the human fetus including some conducted on exteriorised fetuses undergoing termination by hysterotomy (Nyberg and Westin, 1962; Rudolph et al., 1971). Pressure data has been obtained from the human fetus for normal human hearts and in cardiac disease (Johnson et al., 2000; Johnson et al., 1992; Johnson, 1992). However, the vast majority of cardiac functional data in the human fetus has been obtained by non-invasive means, which has almost exclusively been by echocardiography. This article will review some of the techniques that may be used to evaluate fetal cardiac function and will also emphasise some of the limitations of such techniques.