OC29.02: Prevalence of an aberrant right subclavian artery (ARSA) in normal fetuses: a new soft marker for trisomy 21 risk assessment


Aim of the study

An ARSA is diagnosed when the vessel arises separately from the aortic arch and courses behind the trachea, instead of from the brachiocephalic trunk. In the fetus it can be detected in the three-vessel-trachea view using color Doppler. In a previous study we have observed that an ARSA is found in 35% of all second and third trimester fetuses with Down's syndrome (DS). The aim of the present study was to find out the prevalence of this normal variant in the fetal population.


In an 8-month period 908 consecutive fetuses between 15 and 34 weeks without fetal malformations were examined at one center for prenatal diagnosis. The course of the right subclavian artery (RSA) was documented on every fetus. When an ARSA was detected invasive procedure was offered to the patient.


The RSA arose normally in 892 fetuses and was aberrant in 14 cases. In two cases no visualization was possible owing to maternal wall thickness. Invasive procedure was performed in 9/14 cases. In one of these fetuses with an additional intracardiac echogenic focus (30 y patient) a trisomy 21 was detected.


An aberrant right subclavian artery could be used as an additional soft marker for DS during second and third trimester screening. The prevalence of 1.4% (13/905) in the normal population and the previous observation of 35% prevalence in DS, lead to a Likelihood Ratio (LR) of 25 for this new marker. Further studies are needed to confirm our observations.