Gestational age‐adjusted trends and reference intervals of the Modified Myocardial Performance Index (Mod‐MPI) and its components, with its interpretation in the context of established cardiac physiological principles

OBJECTIVE: The objective of this study is to establish gestational age-adjusted reference intervals and trends of the modified myocardial performance index (Mod-MPI), isovolumetric contraction time (ICT), isovolumetric relaxation time (IRT), and ejection time (ET) in pregnancy METHODS: A cross-sectional study using Doppler echocardiography to determine the Mod-MPI was performed on 419 fetuses from 20 to 38 weeks of gestation. Doppler signals of the opening and closing of the mitral and aortic valves were used as landmarks to determine the ICT, IRT, and ET. The Mod-MPI was modeled using fractional polynomials and the exponential-normal model. RESULTS: The Mod-MPI was relatively constant from 20 to 26 weeks and thereafter steadily decreased with advancing gestational age. ICT and ET remained constant, whereas IRT decreased with advancing gestation similar to the Mod-MPI. CONCLUSION: Reference intervals of the Mod-MPI evaluating fetal cardiac function have been established. Maturational and developmental alterations in the myocardial performance in utero resulting in better ventricular compliance is most likely responsible for the decreasing trend of the Mod-MPI noted with advancing gestation.