Assessment of fetal cardiac function using the modified myocardial performance index in fetuses with growth restriction: a prospective observational study

Background: Accurate differentiation between constitutionally small fetuses and those affected by true fetal growth restriction (FGR) remains a major clinical challenge, particularly in fetuses with estimated fetal weight between the 3rd and 10th percentiles. Conventional Doppler parameters may remain normal until late stages of placental insufficiency. The modified myocardial performance index (M-MPI) has been proposed as a sensitive marker of early fetal cardiac dysfunction. Methods: This prospective observational study included 157 singleton pregnancies at ≥32 weeks of gestation. Fetuses were classified according to the Delphi consensus criteria into three groups based on estimated fetal weight percentiles: <3rd percentile (n = 51), 3rd–10th percentile (n = 56), and >10th percentile (n = 50). Fetal biometry, amniotic fluid index, umbilical artery and middle cerebral artery Doppler measurements were obtained. Fetal cardiac function was assessed using the modified myocardial performance index. Delivery outcomes were recorded. Comparisons among groups were performed using appropriate statistical tests. Results: Maternal demographic and obstetric characteristics were similar among groups. Umbilical artery Doppler, middle cerebral artery Doppler, cerebroplacental ratio, and amniotic fluid index did not differ significantly between groups (all p > 0.05). In contrast, both fetuses below the 3rd percentile and those between the 3rd and 10th percentiles exhibited significantly prolonged isovolumetric contraction and relaxation times, shortened ejection time, and increased M-MPI values compared with fetuses above the 10th percentile (p < 0.05). No significant differences in M-MPI parameters were observed between the <3rd percentile and 3rd–10th percentile groups. Conclusions: Fetuses with estimated fetal weight below the 10th percentile, including those within the borderline 3rd–10th percentile range, demonstrate subclinical cardiac dysfunction despite normal conventional Doppler findings. Assessment of the modified myocardial performance index may provide valuable additional information in the evaluation and surveillance of suspected fetal growth restriction.