Are second-trimester minor sonographic markers for Down syndrome useful in patients who have undergone first-trimester combined screening?

Abstract

We sought to determine efficacy of minor markers for detection of Down syndrome (DS) in a population prescreened with first-trimester combined screening (FTS). FTS was modified using established likelihood ratios to generate a new composite risk (NCR). Of 3845 women, 390 had ≥1 marker. There were 10/3845 cases of DS; 3 were among patients with low-risk FTS (n = 3727). In 55 patients, NCR adjusted the risk from low to high without increasing detection rate. NCR did not modify risk to allow for detection of the 3 DS among patients with low-risk FTS even though 2 of these fetuses had 1 minor marker each. There were 7 DS among patients with high-risk FTS (n = 118). Use of NCR increased positive predictive value from 7/118 (5.1%) to 7/53 (13.2%). Screening for minor markers is useful in patients with high-risk FTS. It is of questionable benefit in patients with low-risk FTS.