What are the novel findings of this work?We provide novel reference ranges for fetal cardiac, atrial and ventricular relative size and sphericity, ventricular dominance, wall thickness asymmetry and relative wall thickness, from 18 to 41 weeks' gestation, created from a prospective cohort of low-risk singleton pregnancies undergoing fetal echocardiography following standardized methodology. What are the clinical implications of this work?The provided nomograms constitute a clinically useful tool for the accurate assessment of fetal cardiac remodeling patterns in different clinical scenarios, including congenital heart disease, which could contribute to the better understanding and monitoring of fetal adaptations to an adverse environment.

Fetal Heart Quantification (FetalHQ®) is a novel speckle tracking software that permits the study of global and regional ventricular shape and function from a 2D four-chamber-view loop. The 4D-Spatio Temporal Image Correlation (STIC) modality enables the offline analysis of optimized and perfectly aligned cardiac planes. We aimed to evaluate the feasibility and reproducibility of 4D-STIC speckle tracking echocardiography (STE) using FetalHQ® and to compare it to 2D STE. We conducted a prospective study including 31 low-risk singleton pregnancies between 20 and 40 weeks of gestation. Four-chamber view volumes and 2D clips were acquired with an apex pointing at 45° and with a frame rate higher than 60 Hz. Morphometric and functional echocardiography was performed by FetalHQ®. Intra- and interobserver reproducibility were evaluated by the intraclass correlation coefficient (ICC). Our results showed excellent reproducibility (ICC > 0.900) for morphometric evaluation (biventricular area, longitudinal and transverse diameters). Reproducibility was also good (ICC > 0.800) for functional evaluation (biventricular strain, Fractional Area Change, left ventricle volumes, ejection fraction and cardiac output). On the contrary, the study of the sphericity index and shortening fraction of the different ventricular segments showed lower reproducibility (ICC < 0.800). To conclude, 4D-STIC is feasible, reproducible and comparable to 2D echocardiography for the assessment of cardiac morphometry and function.