It has been shown that the modified myocardial performance index (Mod-MPI) is associated with higher reproducibility than conventional MPI because it uses mitral and aortic valve ‘clicks’ to calculate each time period. We aimed to construct normal reference values for the Mod-MPI after 19 weeks gestation.

Numerous fetal and pregnancy-associated conditions have a considerable impact on the fetal heart. Consequently, evaluation of cardiac function has been increasingly performed in order to assist in clinical decision-making. To this end, the use of different fetal cardiac parameters has been proposed, such as shortening and ejection fractions, tricuspid regurgitation, and abnormal flow in the aortic isthmus. However, in clinical practice, most of the cardiac indices proposed are of limited applicability, owing to low interobserver reproducibility.

The myocardial performance index (MPI) was first proposed by Tei et al. for the evaluation of heart function in adults with amyloidosis. The MPI is the ratio between the duration of the isovolumetric period (composed of two periods – contraction and relaxation) and the duration of the ejection period in the cardiac ventricle. Abnormal cardiac function is associated with a prolongation of the isovolumetric period and a reduction in ejection time, thus resulting in an increase in the MPI. For the original calculation, Tei et al. proposed the acquisition of two waveforms in different locations: first, below the atrioventricular valve to record the E/A waveform for calculation of the isovolumetric periods, and second, in the outflow tracks for the ejection period.

Although the MPI has become part of routine clinical assessment in newborns, in fetuses it is still under evaluation. Several authors have calculated the MPI in fetuses using the originally described technique, but the results show wide variability in the values reported for normal fetuses. To improve the performance of this technique, Friedman et al. suggested that the MPI in the left ventricle could be evaluated during the same Doppler waveform. This approach is feasible because the aorta emerges very close to the mitral valve; furthermore, it allows direct and individual measurement of isovolumetric contraction time (ICT) and isovolumetric relaxation time (IRT). However, this approach does not solve an important drawback for calculation of the MPI – i.e. the absence of clear landmarks delineating the three periods used for this calculation. A substantial improvement was achieved by Raboisson et al., who first used the Doppler echo (‘click’) of the opening of the aortic valve (AV) as a landmark to better estimate the limits of the ejection period. As a further development of this idea, we recently proposed a modified MPI (Mod-MPI) in the left ventricle, which uses the opening and closing clicks of the mitral valve (MV) and AV to clearly define the three time periods used for the MPI. This Mod- MPI significantly improved interobserver reproducibility, as compared with the standard MPI calculation.