Prospective longitudinal assessment of the fetal left modified Myocardial Performance Index

Introduction: The fetal left modified Myocardial Performance Index (Mod-myocardial performance index (MPI)) is a measure of systolic versus diastolic time intervals obtained from a single cardiac cycle with ultrasound. It is a measure of global ventricular function and has been investigated for potential utility in fetal conditions associated with cardiac dysfunction.

Objectives: The objective of this study is to compare values from a precisely replicated fetal left Mod-MPI technique to published reference ranges.

Methods: Three hundred and sixty-five nulliparae prospectively underwent fetal left Mod-MPI measurement at 27⁺⁰-29⁺⁰ and 35⁺⁰-37⁺⁰ weeks' gestation. Measurements from pregnancies complicated by gestational diabetes mellitus, preeclampsia, or a small-for-gestational-age (<10th centile) infant were excluded. Mod-MPI values were compared with three published references created using similar measurement techniques.

Results: Compared with one selected reference, at 29⁺⁰ and 35⁺⁰-37⁺⁰ weeks' gestation, 90-100% of our values fell within the 5th-95th percentile range as expected. Thus, this reference range was validated for our population in late pregnancy. However, the expected level of concordance was not seen at 27⁺⁰-28⁺⁶ weeks'. The other two references to which we compared our Mod-MPI values demonstrated poor concordance, especially at 27⁺⁰-29⁺⁰ weeks'. Pearson interobserver correlation was also improved at 35⁺⁰-37⁺⁰ weeks' at 0.434, compared with 0.083 at 27⁺⁰-29⁺⁰ weeks' gestation.

Conclusions: Concordance and interobserver variability between our cohort and similar populations were both improved at 35⁺⁰-37⁺⁰ weeks' compared with 27⁺⁰-29⁺⁰ weeks' gestation. Overall, variable Mod-MPI reproducibility across gestations limits clinical application, especially earlier in pregnancy. Manual Mod-MPI measurement should be considered most reliable in late pregnancy until automated MPI measurement is possible.