Analysis of secondary ultrasound markers in the first trimester before chorionic villus sampling.

Objective: To evaluate detection and false-positive rates of the ultrasound markers-nasal bone (NB), ductus venosus (DV) flow and tricuspid regurgitation (TR)-during the first trimester in a population at high genetic risk, and to study the influence of a two-stage screening policy alter previous combined screening on the rate of invasive procedures.

Methods: A total of 333 chorionic villus samples were obtained in singleton pregnancies. Before biopsy, the ultrasound markers-NB, DV, and TR-were assessed, although the findings were not used to recalculate the previously determined risk for Down syndrome.