Normal fetal echocardiography ratios - a multicenter cross-sectional retrospective study.

Objectives: Normal fetal echocardiography ratios reflect blood flow balance and developmental patterns, providing a basis for more accurate diagnosis and prediction of congenital heart disease in fetuses. Despite its significance, standardized studies with ample samples are lacking. We aim to establish reference ranges for fetal cardiac structural parameters and hemodynamics using extensive multicenter data, including 11 ratios, and to clarify how these ratios change with gestational age.

Methods: This is a multicenter cross-sectional retrospective study. 23,313 normal fetal echocardiographic examinations were enrolled from three medical centers. Analysis included 11 fetal cardiac-related ratios, such as right/left heart diameter ratio, mitral and tricuspid valve E/A-wave velocity ratio. To determine the reference ranges for various ratios across different gestational ages, a nonparametric quantile regression model, which does not presuppose normality, was utilized. The study investigated how the ratios change with gestational age by examining nonparametric regression plots and their first and second derivatives.

Results: We established normal percentile reference ranges for 11 ratios at each gestational day. Analysis of ratio changes across gestation reveals several key patterns: The right heart system consistently dominates, with the right heart/left heart internal diameter ratio accelerating from 21.7 weeks of gestation; throughout fetal development, the E/A ratio of the mitral and tricuspid valves initially remains below one but increases progressively with gestational age, both reaching their maximum growth rates at week 25.7.

Conclusions: This study provides new references for routine obstetric screening, may enhance the understanding of the growth and developmental patterns of normal fetal hearts.