The presence during the prenatal period of a cystic mass with multiple septa with multiple, asymmetric, thin-walled cysts near the posterior aspect of the neck. Fetal cystic hygroma can be defined as nuchal translucency with or without septations measuring greater than 3.0 mm. Increased NT refers to a measurement above the 95th centile, and the term is used irrespective of whether the collection of fluid is septated or not, and whether it is confined to the neck or envelopes the whole fetus. After 14 weeks, increased NT usually resolves, but in some cases it evolves into nuchal edema or cystic hygromas.