To examine whether combining the dichotomous assessment of the a-wave and the Ductus venosus (DV) PIV measurement improves first-trimester-screening performance. Retrospective study performed at the University Hospital of Tuebingen based on singleton pregnancies that underwent first-trimester-screening including DV flow assessment. In each case, the risk of Trisomy 21 was calculated based on maternal age, fetal NT, and DV flow either as dichotomous classification of the a-wave, as measurement of the DV PIV, or both. There were 5280 euploid fetuses and 127 fetuses with Trisomy 21. The DV a-wave was reversed in 2.3% and 66.1% in the euploid and Trisomy 21 cases, respectively. The DV PIV measurements were above the 95th percentile in 8.3% and 77.2% the euploid and Trisomy 21 cases, respectively. For a FPR of 3%, DR for Trisomy 21 based on maternal age, fetal NT and DV flow is about 87% irrespective of whether DV is examined as a continuous or dichotomous variable. The combination of both resulted in a small decrease at 3% FPR. Assessment of the DV a-wave and the DV PIV result in similar DRs. Combining these two approaches does not appear to improve their individual screening performance.