Abnormal nuchal translucency: residual risk with normal cell-free DNA screening.

To determine the proportion of genetic abnormalities that could be identified by cell-free DNA screening in pregnancies with an abnormal nuchal translucency. From 2015-2017, pregnancies with nuchal translucency ≥ 3.0 mm on ultrasounds were identified. Pregnancies with genetic testing results were included, whether or not cell-free DNA screening was performed. Comparisons of the proportion of genetic abnormalities detectable on cell-free DNA screening versus not detectable were made based on nuchal translucency values (3.0-3.4 mm; ≥3.5 mm) and maternal age (≥35 versus <35 years). Chi-square analysis, Fisher's exact test, and Mann-Whitney were used for statistical comparison. One hundred ten patients were included, 60 had genetic abnormalities (54.5%), with 44 (73.3%) detectable on cell-free DNA screening and 16 (26.7%) not. In those with nuchal translucency ≥3.5 mm, only 40 of 56 (71.4%) of abnormalities could be detected by cell-free DNA screening. Cell-free DNA screening could identify 27 of 31 abnormalities with nuchal translucency ≥3.5 mm in women ≥35 years but could identify only 13 of 25 genetic abnormalities in younger women (87.1 versus 52.0%;  = .005). A significant proportion of abnormalities in those with nuchal translucency ≥3.5 mm would not be detected by cell-free DNA, especially in younger women.