Objective:To investigate the application of fetal atria septal excursion index (ASEI) combining cardiovascular structure Z-scores in fetuses with redundancy foramen ovale flap (RFOF).Methods:Twenty-two fetuses with RFOF diagnosed by fetal echocardiography in Sir Run Run Shaw Hospital from December 2019 to September 2021 were selected as the RFOF group and 62 normal fetuses as the control group. The movement of the foramen ovale valve was observed in the four chamber view, and the maximum distance of the foramen ovale valve bulging, the total length of the atrial septum, the foramen ovale diameter, the diameters of the aortic valve, the pulmonary valve, the ascending aorta, the aortic isthmus, the descending aorta and the left and right ventricular areas were measured. ASEI, foramen ovale diameter, foramen ovale valve excursion distance, the ratio of foramen ovale diameter to total atrial septum length, aortic valvular annular diameter Z-score(AOV Z-score), pulmonary valvular annular diameter Z-score(PV Z-score), ascending aorta diameter Z-score(AOA Z-score), ascending aorta diameter Z-score (AOA Z-score), aortic isthmus Z-score (AOI Z-score), descending aorta diameter Z-score (AOD Z-score), diastolic right ventricular area Z-score (RV area Z-score) and diastolic left ventricular area Z-score(LV area Z-score) were compared between the two groups. RFOF fetuses were followed up to observe the prognosis.Results:There were significant differences in fetal ASEI, foramen ovale diameter, foramen ovale valve excursion distance, the ratio of foramen ovale diameter to total atrial septum length, AOV Z-score, PV Z-score, AOA Z-score, AOI Z-score, AOD Z-score and LV area Z-score between RFOF group and control group (all P<0.05), but there was no significant difference in RV area Z-score ( P>0.05). Postnatal follow-up outcomes in RFOF group indicated that 17 of 22 cases (77.3%) had live birth, five cases (22.7%) were lost at follow-up. Twelve of 17 live birth cases (70.5%) showed structurally normal heart by postnatal echocardiography, 3 cases (17.6%) showed mild coarctation of the aorta with nonsignificant hemodynamics under clinical follow-up, 2 cases (11.8%) were diagnosed with coarctation of the aorta, pulmonary artery dilation and atrial septal defect, and died after operation, of which one case died of infections pneumonia after operation. Another case was born prematurely at 36 + 4 weeks with a birth weight of 2 650 g, and neotal echocardiography showed ventricular septal defect, atrial septal defect and patent ductus arteriosus. Conclusions:ASEI can quantitatively evaluate the behavior of foramen ovale valve mobility and in combination with Z-scores of cardiovascular structures can be used to assess the morphological changes of fetal hearts. Although some fetuses with RFOF demonstrate left and right ventricular disproportion and coarctation of the aorta in fetal echocardiography, most fetuses have a good prognosis.