Objective To investigate the clinical value of ultrasound diagnosis of fetal right aortic arch (RAA).Methods From March 5,2009 to September 2,2012,18 600 pregnant women in three hospitals in Foshan City,Guangdong Province,were divided as RAA high-risk group (n=5000) and low-risk group (n =13 600).During 18 to 42 gestational weeks,detailed ultrasound examinations of fetal aortic arch were done.All babies received echocardiography,CT or MRI within 15 months after birth to observe the cardiovascular condition,and aborted fetus was autopsied.RAA type,complicated structural abnormality and pregnancy outcomes between the two groups were compared with Chi-square test.Results Fifteen fetal RAA were diagnosed prenatally in the low-risk group,and the detection rate was 0.11% (15/13 600),which was lower than that in the high-risk group (0.60%,30/5000)(x2=98.20,P<0.01).The correct rate of prenatal ultrasound diagnosis of RAA was 96% (43/45),while the other two cases were diagnosed as RAA with aberrant left subclavian artery and confirmed to be double aortic arch and RAA with mirror image after birth.In the high-risk group,the incidence of RAA with mirror image,cardiac and extra-cardiac malformation was 73%(22/30),67%(20/30) and 27%(8/30),respectively,which were higher than those in the low-risk group(0/15,1/15 and 0/15)(x2 =30.000,25.200 and 28.000,P<0.01 respectively).The incidence of RAA with aberrant left subclavian artery and the 15-month survival rate of RAA infants in the high risk group was lower than those in the low-risk group [20% (6/30) vs 12/15,40% (12/30) vs 15/15] (x2=7.700 and 15.610,P<0.05,respectively).Conclusions The incidence of fetal RAA is higher in the high-risk pregnant women than in the low-risk pregnant women,and babies often complicated with other malformations with poor prognosis. Key words: Ultrasonography, prenatal; Aorta, thoracic; Congenital abnormalities; Vascular malformations ; Pregnancy