P01.01: Aberrant right subclavian artery (ARSA) in fetuses with trisomy 21

Abstract

Objective: An ARSA is diagnosed when the vessel arises separately from the aortic arch and courses behind the trachea, instead of from the brachiocephalic trunk. It is detected by applying color Doppler at the level of the three-vessel-trachea view. An ARSA is found in approx. 1.5% of the normal population and was described to be more common in fetuses with Trisomy 21. The aim of the present study was to find out the prevalence of this vascular variant in fetuses with Trisomy 21. Patients: In the four years study (2004-2008) fetuses with trisomy 21 between 11 weeks and term and a documented course of the right subclavian artery (RSA) were included in the evaluation. Results: A total of 66 fetuses could be assessed and an ARSA was found in 13 cases (19.6%). The prevalence was the same in the group undergoing 11-14 weeks screening (7/33 = 21%). Conclusions: This study confirms earlier observations on the common finding of an ARSA in fetuses with trisomy 21, but the prevalence is lower than first described. 20% prevalence in trisomy 21 fetuses versus 1,5% in the normal population results in a likelihood ratio of 13× increased risk. This sign can be added to first and second trimester genetic scan. P01.02 Down syndrome screening using first trimester combined tests and conditional use of femur length at routine anomaly scan Objective: To evaluate the performance of contingent use of femur length at routine mid-trimester scan in screening for Down syndrome (DS) in women who had previously undergone first trimester combined screening, with disclosure of risk estimates. Material and methods: This was a simulation study based on the results of a prospective trial of screening for DS using first-trimester combined screening followed by second-trimester ultrasound examination in an unselected population (Rozenberg et al. 2006). Using estimates from the literature, a simulation study was undertaken to evaluate the performance of a contingent screening, based on adding short femur length (FL) at 20-24 weeks as a soft marker in women at intermediate risk on the basis of their first trimester screening results. Sensitivity (Se) and specificity (Spe), detection rates (DR) and false positive rates (FPR) of this contingent use of femur length for the diagnosis of DS were computed. Results: Simulations were computed based on a total of 21,492 patients included. The median maternal age was 30.7 years (range 18.0-46.3). The median gestational age at ultrasound was 12 + 3 weeks (range: 11 + 0; 13 + 6). Contingent screening allowed for an improvement in screening performance. For example, choosing a first trimester risk cutoff of 1/100 and a second trimester risk cutoff of 1/1000 for the use of FL, would allow a Se of 88.4% at a 3% FPR. A first trimester risk cutoff of 1/200 and a second trimester risk cutoff of 1/1000 for the use of FL, would allow a Se of 92.3% at a 4% FPR. Conclusion: This study demonstrates that a sequential screening approach can be used with ultrasound soft markers. Such approach would provide the potential for...

Second‐trimester fetal aberrant right subclavian artery: original study, systematic review and meta‐analysis of performance in detection of Down syndrome

“…Ultrasound screening for Down syndrome is based on the observation that most fetuses with chromosomal abnormalities have major structural malformations or minor anomalies (markers) that can be detected using ultrasound. Interest in prenatal assessment of fetal aberrant right subclavian artery (ARSA) has increased because of the known association between this condition and Down syndrome and other congenital anomalies. Ultrasound assessment of ARSA is performed in the axial plane at the level of the three vessels and trachea view, although it can also be observed in the longitudinal and coronal planes (Figure ); however, feasibility in non‐axial planes has not been described.…”

“…Several recent studies have estimated the prevalence of fetal ARSA in healthy fetuses and in Down syndrome fetuses and assessed the usefulness of ARSA as an ultrasound marker for Down syndrome in the second trimester of pregnancy. The results reflect a wide range of prevalence values in Down syndrome fetuses (8–37%) and discrepancies in the positive likelihood ratio (LR+), depending on whether ARSA is an isolated anomaly (LR+: 0–29.6) or a non‐isolated anomaly (LR+: 12.6–42.04). The limitations of these studies include a lack of data on the prevalence of Down syndrome and on the presence of ARSA as an isolated/non‐isolated finding.…”