Tetraploidy with hydrops fetalis, cystic nuchal hygroma and 90, XX karyotype.

In the present report we describe a mid-trimester Turner fetus with cystic nuchal hygroma, hydrops fetalis and 90, XX karyotype. This observation suggests that the development of a typical Turner syndrome in humans is apparently caused by a specific autosome/X chromosome ratio (44:1 in 45, X patients or 88:2 in the present fetus) rather than by an X-chromosome monosomy.