Objective: There is a need for standardized reference values for cardiac dimensions in prenatal life. The objective of the present study was to construct nomograms for fetal cardiac dimensions using a well-defined echocardiographic methodology in a low-risk population. Methods: This is a prospective cohort study including 602 low-risk singleton pregnancies undergoing a standardized fetal echocardiography to accurately assess fetal cardiac, ventricular, and atrial dimensions. Parametric regressions were tested to model each measurement against gestational age from 18 to 41 weeks of gestation. Results: Nomograms were constructed for fetal cardiac dimensions (transverse and longitudinal diameters and areas) of the whole heart, atria, and ventricles, as well as myocardial wall thicknesses. All dimensions showed a progressive increase with gestational age. The best model for most parameters was a second-degree linear polynomial.Fetal cardiac, ventricular, and atrial diameters and areas were successfully obtained in 98.6% of the fetuses, while myocardial wall thicknesses could be obtained in 96.5% of the population. The results showed excellent interobserver and intraobserver reproducibility (intraclass correlation coefficient, ICC > 0.811 and ICC > 0.957, respectively). Conclusions: We provide standardized and comprehensively evaluated reference values for fetal cardiac morphometric parameters across gestation in a low-risk population. These nomograms would enable the early identification of different patterns of fetal cardiac remodeling.

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.