Objective:To explore the application value of two-dimensional speckle tracking echocardiography (2D-STE) in measuring the global longitudinal peak strain of the right atrium (PRAGLS) in normal fetuses and evaluating PRAGLS in assessing right atrial function in fetuses with moderate and severe tricuspid regurgitation (TR).Methods:A total of 25 fetuses diagnosed with moderate and severe TR, who underwent fetal echocardiography at Run Run Shaw Hospital, Zhejiang University College of Medicine between October 2020 and May 2022, were selected as the case group. Their gestational age ranged from 25.00(24.00, 30.00)weeks. Additionally, 100 normal singleton fetuses were chosen as the control group, with a gestational age of 25.83(23.00, 28.75)weeks. Standard basal or apical four-chamber clips were acquired and inputted into TOMTEC-ARENA offline cardiac analysis software for analysis. The fetal PRAGLS values of the two groups were obtained, as well as the routine obstetric ultrasound measurements and fetal echocardiographic parameters of both groups: fetal heart rate (FHR), biparietal diameter (BPD), femur length (FL), aortic annulus inner diameter (AO), pulmonary annulus inner diameter (PA), PA/AO ratio, right atrial end-systolic length (RAESL), right atrial end-systolic diameter (RAESD), right atrial end-systolic area (RAESA), right ventricular end-diastolic diameter (RVEDD), and tricuspid annular plane systolic excursion (TAPSE). The peak TR velocity and pressure gradient were simultaneously measured in the case group.The differences in fetal PRAGLS and other parameters between the two groups were compared and analyzed. The correlation between fetal PRAGLS and gestational age (GA) and routine measurements was assessed for both groups. Intra- and inter-observer repeatability tests were conducted using the intragroup correlation coefficient (ICC).Results:A significant difference in PRAGLS was observed between the two groups ( t=11.55, P<0.01). The TAPSE difference between the two groups was also statistically significant ( Z=3.45, P=0.01). Notable differences were found in AO, PA, PA/AO, RAESL, RAESD, and RAESA between the two groups (all P<0.05), but no significant differences were identified in age, GA, FHR, BPD, FL, and RVEDD between the two groups (all P>0.05). PRAGLS in the control group exhibited a moderate negative correlation with GA ( r=-0.47, P<0.01) and were correlated with BPD, FL, AO, PA, RAESL, RAESD, RAESA, and RVEDD ( r=-0.50, -0.46, -0.39, -0.43, -0.45, -0.36, -0.43, -0.32, all P<0.05). No significant correlation was observed with maternal age, FHR, PA/AO, and TAPSE (all P>0.05). No significant correlation between PRAGLS and GA or other conventional parameters was found in the case group (all P>0.05). The inter-measurer and intra-measurer ICC of PRAGLS in the control group were 0.87 and 0.79, respectively, while the inter-measurer and intra-measurer ICC of PRAGLS in the case group were 0.94 and 0.97, respectively, demonstrating good consistency. Conclusions:2D-STE exhibits strong feasibility and reproducibility in assessing fetal atrial function.Fetuses with moderate and severe TR display decreased PRAGLS, suggesting impaired right atrial reservoir function. Right atrial strain introduces a novel method for evaluating fetal cardiac function.