To evaluate the application value of quantification of the distance and angle between the ductal arch and aortic arch in the diagnosis of fetal right aortic arch (RAA).

Fifty-two fetuses with isolated RAA were selected as a study group (RAA group) and randomly paired with 120 normal cases as a control group. The diameter of the ductus arteriosus and the aortic arch as well as the distance and the angle (AP angle) between the two arches was measured on the three vessel views (3VT view). Statistical analysis was performed for comparison of each parameter between the two groups.

Compared with the control group, the distance between the ductus arteriosus and the aortic arch increased [4.86 (4.16~5.74) mm vs 1.59 (1.38~1.76) mm], and the AP angle decreased [(12.96±1.83)° vs (22.14±1.35)°] in the RAA group (Z=-10.416, P<0.05; t=32.481, P<0.05). There was no significant difference between the two groups in the values and ratios of the diameters between the ductus arteriosus and the aortic arch, diameters of the aorta and pulmonary artery, or blood flow velocities across the aortic valve and pulmonary valve (P>0.05). There were no correlations between the gestational age and the AP angle or the ratio of the diameter of the ductus arteriosus to the aortic arch (RAA group: r=0.148, 0.029, P=0.294, 0.818; control group: r=0.060, 0.108, P=0.514, 0.180), while the distance between the ductus arteriosus and the aortic arch, diameters of the ductus arteriosus and the aortic arch, diameters of the aorta and pulmonary artery, and blood flow velocities across the aortic valve and pulmonary valve were all linearly positively correlated with the gestational age (P<0.05).

Measurements of the distances and angles between the aortic arch and ductal arch in the 3VT view of fetal ultrasonocardiography are simple and feasible, which may have a supplementary role in the diagnosis of fetal RAA with left-sided ductus arteriosus.