Aberrant right subclavian artery: incidence and correlation with other markers of Down syndrome in second-trimester fetuses.

OBJECTIVE: To assess the incidence of aberrant right subclavian artery (ARSA) and other strong markers of Down syndrome and their correlation in a large population of second-trimester Down syndrome fetuses assessed in a tertiary referral center. METHODS: Presence or absence of ARSA and other major ultrasound markers of Down syndrome was assessed in a population of 106 second-trimester Down syndrome fetuses referred to our unit for expert assessment and/or termination of pregnancy after karyotyping performed for positive first- or second-trimester screening or advanced maternal age or on maternal request. All cases in which the diagnosis of Down syndrome followed the ultrasound detection of major anomalies or soft markers were excluded from the study, as were all cases with a gestational age less than 14 + 0 weeks. We searched for the ARSA on the three vessels and trachea view using color or power Doppler. All fetuses underwent a thorough anatomic assessment and fetal echocardiography. The other Down syndrome markers assessed were: absent or hypoplastic nasal bone (NB-), defined as length < 5(th) centile; nuchal fold ≥ 5 mm; and mild pyelectasis (> 5 mm). In addition, the presence of major cardiac and extracardiac defects was recorded. A correlation analysis was then performed in order to investigate possible associations between markers and/or major anomalies. Postmortem or postnatal diagnostic confirmation was available in all cases. RESULTS: The mean (SD) gestational age at ultrasound assessment was 20.4 (4.1) weeks. The incidence of the various variables in the population of Down syndrome fetuses was: ARSA, 25%; NB-, 43%; nuchal fold ≥ 5 mm, 16%; pyelectasis, 17%; major heart defects, 41%; atrioventricular septal defect, 25%; and extracardiac anomaly, 24%. The presence of ARSA did not correlate with any of the other variables. The only positive correlations (P < 0.05) were between NB- and pyelectasis, and between cardiac and extracardiac defects. CONCLUSIONS: This represents the largest Down syndrome population assessed for ARSA. In this series, the incidence of ARSA was 25%, lower than previously reported in much smaller series. Its presence did not correlate with the presence of any other marker or major anomaly, including heart defects.