Testing for Noonan syndrome after increased nuchal translucency

Objective The aim of this study was to report the prevalence of Noonan syndrome (NS) in a cohort of fetuses that presented with increased nuchal translucency (NT) thickness in the first trimester of pregnancy. Methods This is a retrospective chart review. Inclusion criteria: (1) first trimester NT measurement >= 3 mm, (2) normal karyotype by either a CVS or an amniocentesis procedure, and (3) prenatal molecular genetic testing for NS completed. Results with known pathogenic variants were considered positive, while those with variants of unknown clinical significance, or with no variants, were considered negative. Results A total of 804 fetuses had an NT measurement of >= 3 mm, with a median NT thickness of 3.6 mm. Of these, 302 had karyotyping by CVS or amniocentesis, 200 (66.23%) with normal results. Of fetuses with a normal karyotype, 39 with a median NT thickness of 4.0 mm had a NS gene sequencing panel done, and 161 fetuses with a mean NT thickness of 4.3 mm were not tested for NS (p = 0.05). Of the 39 fetuses who were tested for NS, four (10.3%) had variants consistent with this diagnosis. Conclusion In euploid fetuses, increased NT is associated with a 10% risk of NS. (C) 2017 John Wiley & Sons, Ltd.