In this study we describe the prenatal characteristics of Noonan syndrome and its associated syndromes called Rasopathies in 40 fetuses with a pathogenic variant in one of the Rasopathy genes. The most common feature is increased nuchal translucency (NT). Based on our data we suggest genetic testing of fetuses with an isolated persistent NT ≥5.0 mm (after excluding chromosomal aberrations). We also recommend genetic testing when NT is ≥3.5 mm with at least one of the following anomalies: distended jugular lymph sacs, hydrops fetalis, polyhydramnios, pleural effusion and/or cardiac defects. Renal anomalies and ascites were poor predictors of finding a pathogenic Rasopathy variant. No clear genotype-phenotype correlation was detected. (By Kyra Stuurman, https://jmg.bmj.com/content/early/2019/04/30/jmedgenet-2018-105746 )