Detecting Fetal Heart Stress in Growth Restricted Fetuses

Fetal growth restriction (FGR) remains a significant challenge for obstetricians managing high-risk pregnancies. Recent evidence highlights that monitoring the Fetal Myocardial Performance Index (MPI) provides critical insights into subclinical cardiac dysfunction. This index serves as a global measure of both systolic and diastolic ventricular function. It is particularly useful when conventional Doppler parameters appear normal. Consequently, understanding these cardiac changes allows for better risk stratification in fetuses with restricted growth.

Evaluating Cardiac Dysfunction in FGR

A comprehensive systematic review analyzed data from over 1,500 fetuses to assess myocardial performance. The study focused on how placental insufficiency impacts heart function. Specifically, researchers observed that fetuses with growth restriction exhibit significant biventricular dysfunction. Both the left and right ventricles show signs of impairment compared to healthy controls. Moreover, the most striking finding was the prolongation of the isovolumetric relaxation time. This parameter indicates a failure in myocardial relaxation during the early stages of the cardiac cycle.

Clinical Utility of the Fetal Myocardial Performance Index

Clinicians often rely on the E/A ratio to evaluate diastolic health. However, the Fetal Myocardial Performance Index appears to be a more sensitive marker for detecting early compromise. While the left ventricle shows the most pronounced changes, the right ventricle also experiences significant stress. Furthermore, these alterations affect both early-onset and late-onset FGR phenotypes. Therefore, integrating MPI into routine surveillance could improve outcomes. This approach helps identify fetuses at risk of cardiovascular remodeling before severe hypoxia occurs.

Timing and Diagnosis in Pregnancy

Early-onset growth restriction typically involves more severe cardiac impairment than late-onset cases. Nonetheless, even late-onset fetuses show measurable changes in myocardial performance. Practitioners should note that prolonged relaxation times often precede changes in umbilical artery flow. Additionally, stricter diagnostic criteria for FGR consistently confirm these cardiac findings. The analysis did detect some publication bias regarding left-sided measurements. Finally, using this index as an adjunctive tool enhances the overall monitoring strategy for complex pregnancies.

Frequently Asked Questions

Q1: Why is the IRT more sensitive than the E/A ratio in FGR?

The isovolumetric relaxation time (IRT) reflects the heart’s ability to relax before filling. In growth-restricted fetuses, increased afterload and hypoxia lead to early diastolic stiffness. This stiffness causes the IRT to prolong significantly before the filling velocities show abnormal patterns.

Q2: Does the myocardial performance index differ between early and late FGR?

Both phenotypes exhibit cardiac dysfunction. However, early-onset FGR often shows a trend toward more severe impairment due to the prolonged duration of placental insufficiency. Despite this difference, the index remains a valuable marker for both groups in identifying subclinical cardiac stress.

References

1. Sirico A et al. Left and right myocardial performance indices in growth-restricted fetuses: systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2026 May 11. doi: 10.1002/uog.70233. PMID: 42113889.
2. Zhang J et al. The Significance of the Myocardial Performance Index and Fetal Doppler Abnormalities in Growth-Restricted Fetuses: A Systematic Review. PMC. 2024 Oct 28.
3. Nguyen T et al. Assessment of myocardial performance index in late-onset fetal growth restriction. PubMed. 2021 May 15.