Aberrant right subclavian artery at 11 + 0 to 13 + 6 weeks of gestation in chromosomally normal and abnormal fetuses.

OBJECTIVES To establish the feasibility of examining the subclavian artery at 11 + 0 to 13 + 6 weeks of gestation, and to determine the prevalence of aberrant right subclavian artery (ARSA) in chromosomally normal and chromosomally abnormal fetuses. METHODS Fetal echocardiography was performed prospectively in 516 patients before chorionic villus sampling at 11 + 0 to 13 + 6 weeks of gestation. Transabdominal sonography was carried out, and color flow mapping was used to identify the right subclavian artery and determine whether this was normal or aberrant (ARSA). Second-trimester fetal echocardiography was also carried out in a subgroup of 183 fetuses. RESULTS The median gestational age was 12 weeks and the median crown-rump length was 68 mm. Successful assessment of the right subclavian artery was achieved in 425/516 (82.4%) cases and the rate of failure to do so was significantly associated with decreasing fetal crown-rump length (r = 0.174, P < 0.001) and increasing maternal body mass index (r = 0.275, P < 0.001). An ARSA was observed in 2/353 (0.6%) fetuses with a normal karyotype, in 4/51 (7.8%) cases with trisomy 21 and in 2/20 (10.0%) with other chromosomal defects. In a subgroup of 183 fetuses examined in both the first and second trimester there were three cases of ARSA observed at both scans and an additional case in which ARSA was detected only at the second scan. CONCLUSIONS Assessment of the position of the right subclavian artery is feasible at the 11 + 0 to 13 + 6-week scan and ARSA is more common in chromosomally abnormal than normal fetuses. However, ARSA in the first trimester is unlikely to be a useful marker of trisomy 21.