Screening performance for trisomy 21 comparing first trimester combined screening and a first trimester contingent screening protocol including ductus venosus and tricuspid flow

Abstract

To compare the standard first trimester combined risk assessment for trisomy 21 with a contingent screening protocol including tricuspid flow and ductus venosus flow. Women with singleton pregnancies and a first trimester combined risk assessment>1:1000 were included. They all had additional assessment of the ductus venosus and the tricuspid flow. We compared screening performance in two screening strategies: (a) First trimester combined screening strategy based on the individual risk results from the routine screening test and (b) Contingent screening strategy based on a combination of the routine test results and additional ultrasound markers. We included 917 women in the study, 894 in the euploid group and 23 in the trisomy 21 group. Using a contingent screening strategy resulted in a significant decrease in screen positive rate from 48.3% to 17.7% (p<0.001) in the studied population. There was no statistical difference in detection rate between the two screening strategies. There is increasing evidence in favour of using additional ultrasound markers as part of contingent screening protocols in the first trimester. We do suggest performing further studies in routine clinical settings to provide validation of the available risk algorithms.