Objective To analyse the main characteristics, associated conditions and outcome of right aortic arch (RAA) detected in fetal life, and to assess if further investigation is required in cases of isolated RAA.

Methods Retrospective observational study of all fetuses diagnosed with a RAA between 2004 and 2012 at a tertiary centre for fetal cardiology.

Results A RAA was identified in 98 fetuses: 27 had normal intracardiac anatomy and 71 were associated with other congenital heart disease (CHD); conotruncal anomalies being the most common. An aberrant left subclavian artery was diagnosed in 18.4% of cases, a double aortic arch in 6.1%, and 12.2% had a vascular ring confirmed after birth. Overall, an extracardiac anomaly was present in 31.6% of the patients and a chromosomal anomaly in 15.3%, with half of the latter cases being 22q11.2 microdeletion. Extracardiac and chromosomal anomalies were more commonly associated with RAA with structural CHD (39.4% and 19.7%, respectively), compared to cases of RAA with normal intracardiac anatomy (11.1% and 3.7%, respectively) (p<0.05). First year mortality was 10.3%, with all deaths being in cases with associated structural CHD.

Conclusions Detailed fetal extracardiac examination should be undertaken in all cases of RAA. Isolated RAA has a good prognosis, and in the majority of the patients it is an asymptomatic vascular variant with a relatively low risk for chromosomal anomaly. The prognosis of RAA with CHD depends on the complexity of the CHD and/or the associated extracardiac anomalies. In these cases, there is a higher risk for chromosomal anomaly, particularly 22q11.2 microdeletion.