Objective: Nuchal translucency. Design: Study of human foetuses. Setting: Institute for Mother and Child Care, Praque, Czech Republic. Conclusion: Nuchal translucency represents accumulation of foetal cerebrospinal fluid diffusing through the ceiling of IV th cerebral ventricle. Relevant nuchal translucency is unspecific marker of foetal circulatory insufficiency and is a „window fenomenon“. In foetuses older than 16 gestati- onal weeks, separation of the intracranial and extracranial space by developing bones and con- nective tissue, prevents formation of nuchal translucency.

        Key words: nuchal translucency, cerebrospinal liquor, intra- and extracranial space, window feno-