Objective:To investigate the clinical value of ultrasonic measurement of left atrium-descending aorta distance in the diagnosis of fetal total anomalous pulmonary venous connection (TAPVC).Methods:Pregnant women who underwent fetal anatomy scans in the second trimester of pregnancy in Central Hospital of Panyu District between January 2018 and June 2019 were included in this study using prospective and case-control study methods. The GE Voluson E8 and Philips EPIQ 7 ultrasound machines were used to measure the left atrium-descending aorta distance in the four-chamber view of the fetal heart. Pulmonary vein was carefully examined. Fetuses with isolated TAPVC were included in the positive group. The pregnancy outcomes were followed up during all participants. 200 healthy fetuses were randomly selected and included in the control group. The correlation between left atrium-descending aorta distance in normal fetuses and gestational weeks was analyzed. The average value of left atrium-descending aorta distances was compared between positive and control groups.Results:A total of 2 156 pregnant women received fetal anatomy scans, with the completion rate of 100%. Among them, 1 786 pregnant women were successfully followed up and 370 were lost to follow up. Among the 1 786 pregnant women, four fetuses were diagnosed with isolated TAPVC, consisting of three fetuses with intracardiac type TAPVC and one fetus with supracardiac type TAPVC, as confirmed by prenatal ultrasound. The left atrium-descending aorta distance in 200 normal fetuses was weakly related to gestational weeks ( r2 = 0.35, P < 0.000 1). The mean left atrium-descending aorta distance in the positive group was significantly greater than that in the control group (5.4 mm vs. 2.1 mm). Conclusion:Ultrasonic measurement of left atrial posterior spatial distance is simple and it is hardly affected by gestational weeks. It is innovative to diagnose TAPVC through quantitative analysis. The widening of left atrium-descending aorta distance has a certain value in suggesting fetal TAPVC. The sample size is small in this study. Multi-center studies involving larger sample sizes are needed to further validate the clinical significance of widened left atrium-descending aorta distance.