Incidence of an Aberrant Right Subclavian Artery on Second-Trimester Sonography in an Unselected Population.

Objectives: The aim of this study was to assess the incidence of an aberrant right subclavian artery (ARSA) among an unselected population during second-trimester sonography and to review the importance of this conotruncal variant as a marker of Down syndrome.

Methods: The presence or absence of an ARSA was assessed in an unselected population of 1913 second-trimester fetuses.

Results: Among the 1913 patients, an ARSA was detected in 20 fetuses (1.04%), all with a normal karyotype. Thirteen of 20 fetuses had an isolated ARSA, and 7 of them were nonisolated. Associated abnormal sonographic findings were an intracardiac echogenic focus (n = 3), a choroid plexus cyst (n = 1), pyelectasis (n = 1) and tetralogy of Fallot (n = 2). One of the cases of tetralogy of Fallot was also associated with a persistent left superior vena cava, a persistent right umbilical vein, hydrocephalus, rhombencephalosynapsis, and unilateral renal agenesis. There were only 2 fetuses with Down syndrome in this group, and both of them had a normal origin of the right subclavian artery.

Conclusions: In an unselected population, an ARSA may be seen less frequently than in a high-risk population and may not be related to Down syndrome. An isolated ARSA is not a sufficient indication for karyotype analysis; it can be managed with noninvasive prenatal testing rather than invasive testing.