Reference Limits for Fetal Biventricular Longitudinal Strain Using Speckle Tracking Echocardiography Across Gestational Age Groups: A Single-Center Study

<b>Background/Objectives:</b> The development of normal fetal cardiac function, a dynamic process that has not yet been precisely documented throughout the literature, is difficult to quantify by classic echocardiography. Our aim was to analyze the function of the fetal myocardium through speckle tracking and establish reference values for global and segmental longitudinal strain for both ventricles in fetuses with a gestational age (GA) between 22 and 39 weeks. <b>Methods:</b> We conducted a prospective study in which 170 fetuses underwent echocardiographic evaluation and those 150 that were eligible for the study underwent offline speckle tracking analysis. <b>Results:</b> A mixed-design ANOVA model with Greenhouse-Geisser correction showed no significant differences in regional strain measurements among GA groups (F [2, 147] = 1.25, <i>p</i> = 0.289) but showed significant differences in regional strain measurements among the right ventricle (RV), left ventricle (LV), and interventricular free wall (Greenhouse-Geisser F [1.3, 195.2] = 45.70, <i>p</i> < 0.001, GG ε = 0.66, original df = 2, 294). The wall-by-segment interaction term of the model was statistically significant for regional strain (Greenhouse-Geisser F [2.7, 394.2] = 27.00, <i>p</i> < 0.001, GG ε = 0.67, original df = 4, 588), while the segment-by-gestational age group term had a tendency toward statistical significance (Greenhouse-Geisser F [3.0, 221.4] = 2.21, <i>p</i> = 0.088, GG ε = 0.75, original df = 4, 294). The results of Welch's ANOVA model showed no significant difference in right-ventricle peak global longitudinal strain (pGLS) between GA groups (F [2.0, 92.2] = 0.52, <i>p</i> = 0.5972) and global longitudinal strain measurements (F [2.0, 89.6] = 27.00, <i>p</i> = 0.3733). <b>Conclusions:</b> The reference values for longitudinal strain, represented by the pGLS for LV, ranged from -20.79 to -8.05 for fetuses with a GA between 22 and 27 weeks, from -20.14 to -8.99 for fetuses with a GA between 28 and 33 weeks, and from -20.19 to -8.88 for fetuses with a GA between 34 and 39 weeks. For RV pGLS, the reference values were between -18.99 and -6.35, also depending on GA. Reference ranges for the large gestational groups studied can help us to recognize subtle changes in fetal cardiac function.